- “Looks good, doesn't it? They're trapped in here. Terrified. Meat for the beast, and there's nothing they can do but wait..... That's all they've been doing for days.... waiting to be picked off. Having nightmares about monsters that can't be killed. But I don't believe in that. I always find a way. I'm the thing that monsters have nightmares about. And right now...you and me are gonna show 'em why.”
- ―Buffy Summers.[src]
A Demon, also called a Hostile Sub-Terrestrial, was a member of a class of supernatural lifeforms native to various Hell dimensions separated from Earth and generally considered to be evil due to their lack of human souls and their destructive tendencies. The term was widely used to describe any creature that was not a god, robot, unmodified human, or standard terrestrial animal. Though individual powers varied between different demon species, most, if not all, demon species possessed greater strength, endurance, and natural abilities than humans.
HistoryThe original and most powerful demons originated eons ago, in godlike extradimensional beings called the Old Ones. The Old Ones lived on Earth during the Primordium Age after they were brought to there from their home dimensions by the Seed of Wonder.
However, as time passed, new, mortal creatures began to appear on Earth and turn on and fight against the demons, and the Old Ones either retreated to other dimensions or interbred with humans, thus diminishing their powers through the generations. According to the Guardians, the last pure demon that walked the Earth during this period was killed by the Scythe.
By modern times, demons native to Earth were not full demons but had a percentage of human heritage, while full demons were native to other dimensions.
The only scientific categorization established for demons was provided by Maggie Walsh, the Head Scientist of the Initiative, who claimed that demons were ranked as a class in the taxonomic hierarchy. Anya Jenkins herself also claimed Sluggoth demons belonged to the same phylum as regular worms.Suvolte demons, Ghora demons, Sluks, the spiders from the Box of Gavrok and even more monstrous forms of existing animals like the Grimslaw Demon, Bug demons, and the Ragna Demon. Also, Kenny was a demon that resembled a Tryannosaurus Rex.
Others demons had vegetative features like the Root monster. Certain species were totally extinct like Illyria's subjects, Sluggoths demons and Ragna demons. However, in the case of the latter two, they were recreated with the magic by Anyanka or by using their DNA by Andrew Wells.
Morality and behaviour
By nature, the majority of demons were innately evil, merciless and unsympathetic towards humans, animals and even some other demons. The reason for this seemed to stem from the lack of a soul which provided a sense of feeling culpable to one's wrong doings, evident by the fact that when humans became vampires they lost the ability to feel any type of general remorse. Confusing the issue was that most demons kill as a natural survival instinct while others commit evil acts for their own recreational enjoyment, to learn something about said victim or religious/cultural reasons. Winifred Burkle even claimed that the act of a cockroach demon planting its offspring into the cranium of a Durslar Beast was "all fine and Darwinian".
For this demons were seen as purely evil creatures with death as the only case for dealing them. There are, however, some cases of perfectly morally sound demon species or individuals such Codger demons, Lister demons, Kwaini demons, Yarbnie demons, Kamal, Jhiera, Val Trepkos, Mellish, Eldre Koh, Ken, Merl, Clem, Whistler and Lorne (who appreciated human culture despite being a member of a violent tribe of demons). It's also shown that a soulless demon can reform so much they form special bonds with humans, such as the vampire Spike who developed a strong love for Slayer, Buffy Summers leading him to fight for his soul back.
Certain demons however demonstrated an evolution in their behavior without resorting to the magic. Kamal was likely a result from a rough species. However, he became the protector of a woman of whom the fate to give birth to a super-heroin.  A species living to Quor'toth became pacifist by observing the filial love between Holtz and Connor.
Certain humans were transformed into demons at a moment of their life and adopted demonic instincts and tendencies. Giles was transformed into Fyarl demon and the longer he stayed as one he began to give in the desire of killing Some Vengeance Demons seemed to believe their acts of murder, torture and extreme unpleasantness were justified by the lesser crimes of humans. For example, Anyanka was a misandrist and did evil deeds based on the wrong-doings of males  while Halfrek focused on the neglect of children.
The Half-breeds and the Half-demons had a varying moral alignment. Although they are also considered worse than the human beings by supremacist demons such as The Scourge, some demonstrated that they were effectively malefic or corrupted by their demonic blood like Billy Blim, Stygian demons, Mal Fraser, Pearl and Nash, while others had naturally human behavior such as Groosalugg and the Lister Clan or they simply rejected their demonic heritage as Beck or Doyle did.
A demon's intelligence was also a factor amongst many species and breeds. A lot of demons such as Vampires, Vengeance Demons and various others possessed intelligence equal to humans while others like Hell Hounds (a variant of this species on Pylea is however tamable), Drokken Beasts and Werewolves during their lupine period were purely, mindlessly feral and could be manipulated as such.
Demons reproduced in diverse and complex ways. Some species, including vampires, Wraith-er Demons, and Werewolves, reproduced by infecting humans and then inhabiting and using their bodies. Others, such as Haxil Beasts and Skilosh Demons, infected humans in order to use their bodies to gestate their young. Some demon species reproduced via sexual intercourse. Some indeterminate number of these species, for instance Brachan and An-Movic Demons, were cross-fertile with humans. Some demon species reproduced via asexual methods, such as budding. Some other appeared to have been created or manufactured by some other entity (magic practitioner, Old One, Power), and do not reproduce on their own. Thaumogenesis would result in the accidental creation of a demon from a spell, often one of a certain great degree where the demon created acted was a way to balance the effect of the spell. 
Most demons were carnivores, mostly preferring human flesh as the best food source. Some demons had diets to a specific substance such as Vampires to blood, Gnarl ate human skin,  the Sluks drank water and humidity in the human bodies,  Norman Pfister under the form of a sentient hive of maggots, devoured his victims from within completely in a few minutes,  Lei-Ach Demons seemed to eat bone marrow,  the Wig Lady had a fixation for humans fed with the Doublemeat Medley, an unidentified species was seen eating human fingers  and various species were known to feed off human hearts. According to Willy, he was able to generate business by selling his demonic patrons fried chicken fingers.
Certain demons have a preference marked for the virgin humans as the demon Machida, Yeska  and Avilas  or the human babies as with Lurconis,  Groxlar Beasts  and a eponymous species. 
Even a half-breed species like Stygian demons showed to be carnivorous.
Other species fed on demon flesh. Lizard demons ate some of their young during hatching season,  Ano-Movic Clan had a tradition to eat the brains of the previous husband of their wives, even if he was a demon, to strengthen the wedding  and Sebassis drank the blood outcome of a slave of his species. 
Some demons practiced cooking considered illegal according to the human criteria. This is evident of restaurants held by Richard Straley  or Torg.  Nahdrah demons had toasts with triton's eye as their own specialty.  Yak urine was one of the options at a demon bar. 
Other demons possessed obscure and somewhat metaphysical needs for sustenance. Thesulac Demons required the presence of insecurity,  Gachnar fed on fear,  Lorophage demons fed on psychological traumas, Soul Eaters were known for feeding on human souls,  Polo and the Smile Time puppets fed on the life force of children,  Shur-hod Demons and Root monster fed on the life force of humans and even others demons like Groosalugg,  Der Kindestod fed specifically on the life force of sick children,  and the Judge needed to "burn" the humanity out of his victim.
Powers and Abilities
The individual powers that demons possessed varied from species to species, but some appeared to be common to most, if not all species:
- Superhuman Strength — Most demons are noticeably physically stronger than humans, although the degree varied from species to species. (Vampires, Vengeance demons, Vyasa, Old Ones, Gronnak demons, Grappler demons, Fyarl demon, M'Fashnik demons etc.)
- Superhuman Durability — Because many demons were native to very harsh environments, their bodies tended to be more resistant to blunt trauma and injuries than human bodies, some species even resistant to bullets. Some demons had armored bodies, although they were relatively vulnerable if a part or all of the armor was damaged or destroyed. (The Beast, Skip's species, Haxil beasts, Vampires, Spike's crew, Space-bug-zompire thing)
- Longetivity/Immortality — A large amount of demon were shown to live longer than humans, and some of them were actually immortal, living for thousands of year without aging. (Vampires, Vengeance demons, Mok'tagar demon, Boone)
- Empathy — The ability to sense or feel emotions. (The Judge, Empath demons, some Vampires, Vengeance demons, Deathwok Clan, Illyria)
- Telepathy — The ability to read minds. (Telepath demons, Splenden beasts, Ethros demons, Sadecki demons, Deathwok Clan)
- Teleportation — The ability to travel to another spot in space without having to transverse the distance between the two points. (Vengeance demons, D'Hoffryn, The Beast, Granok demons, Mok'tagar demons, Stewart Burns)
- Telekinesis — The ability to manipulate objects with the mind. (Vengeance demons, Sadecki demons, Eyghon, Balthazar, Ethros demons)
- Pyrokinesis — The ability to manipulate and conjure fire with the mind. (Local Boy, The Judge, D'Hoffryn, Oden-Tal, Child of Words, Sweet)
- Possession — The ability to take control of another being's body. (Ethros demons, Eyghon, Sluks, Haxil beasts, Ovu Mobani, Child of Words)
- Precognition — The ability to see future events. (Deathwok Clan, Asphyx demons, Drusilla)
- Hypnosis — The ability to manipulate minds. (Thrall demons, some Vampires, Ovu Mobani)
- Voice Manipulation — The ability to manipulate once's or other's voices. (Vengeance demons, Gachnar, The Gentlemen, Arney)
- Invisibility — The ability to make oneself unable to be seen. (Vocah, Der Kindestod, Thesulac demons, Pockla demons)
- Shapeshifting — The ability to alter one's appearance. (Deevak, Eater demons, Ano-Movic demons, Lissa, Wraith-er demons, Vengeance demons, Thricewise)
- Razor-sharp fingernails — The ability of having one's nails sharp enough to wound or shred flesh. (Der Kindestood, Vampires, Turok-Han Vampires, Vahrall demons, Gnarl)
- Giles: “Oh... Anyanka... I-I beseech thee... to Um... In the name of all women scorned... Come before me.....Oh!”
- Anyanka: “Do you have any idea what I do to a man who uses that spell to summon me?”
- — Giles calling forth Anyanka[src]
Certain demons could be beckoned, controlled and directed by specific methods. Tucker Wells trained a group of dangerous hellhounds to hunt prom goers by forcing them to watch prom-related movies. This influenced his younger brother Andrew who could summon demons to attack Buffy by using certain musical instruments such as panpipes and a didgeridoo. These demons include Glarghk Guhl Kashmas'nik demons, Jaarvlen Flesh Eaters (which he claimed was hard to control) and an unnamed species of demon. Halfrek implied that Grimslaw demons were possible to house train, though difficult. 
Some individual demons could be summoned, but not controlled through certain spells. Anyanka could be called via a spell that required her necklace while such worshiped figures such as Machida, Lurconis, "goddess" Yeska and Avilas could be brought upon for a ritual sacrifice and the Queller demons were only summoned to eliminate insane humans.
- Wesley: “And you say this demon wanted cash? That's very unusual”
- Giles: “Demons after money. What ever happened to the still-beating heart of a virgin? No one has any standards anymore.”
- — Giles and Wesley[src]
Most demons possessing near human intelligence adapted to most of the fundamentals of modern human society. They had an underworld status, often sported clothing of the current era (with only some exceptions such as Glory's minions, Sahijhan, D'Hoffryn etc) and took part in human pastimes such as playing poker, though kittens were considered a delicacy, as well as currency, among demons. However, human money was still valued by mainstream demons(but not by others, suchs an unidentified M'Fashnik demon who, despite belonging to a mercenary race, considered money to be nothing more than paper) . Also, pure innocence, especially that of a human child, carried a high deal of street value in hell dimensions.
Despite the degree of modernization, a lot of demons still relied on tribalism. They preferred to stay in packs or clans consisting of members of their own species that practiced ancient rituals and traditions that often involved barbaric sacrifices to their respective deities. They often waged feuds with other clans, as seen with the Viniji and Sahrvin clans, along with bigoted views of humans and demon species closely related to them such as vampires. For example, the Scooby gang found it odd that a vampire and a demon of a totally different species were fighting alongside each other. This was purely a result to Adam training demons to get over their tribal nature and work together for the common evil.
Even though they tended to abandon ancient demonic values and still enjoyed a naturally malevolent status, they did follow some loose rules when socializing with other demons as Spike was briefly rejected by his demon brethren for killing demons after receiving his chip.
Integration into Human Society
Demons like Marc, Norman Pfister, Ken, Vengeance demons, Kathy Newman, Talamour, Doc, the Wig Lady, Wraith-er demons, Lissa, Helen Brucker or Kenny knew perfectly how to disguise and to imitate the customs in the human society.
The Ano-Movic Clan moderated their cult to live in the human society, tolerating even human beings in their family. However, they are still anxious to eat the brains of the previous husband of the wives they divorced .
Certain demons were somewhat progressive, rejecting the ideas inculcated by their species which they considered archaic and prefer to emulate with the humans whom they admire the liberalization like Kathy Newman, Jhiera and the females of her species or Lorne. However, it's not the case of all. Rieff complained that his only contact with the human world was the evening of Halloween.
Interactions with HumansMainstream demons tended to mix with demons of other species as well as tolerate some humans who could accommodate needs such as food from demon friendly bars, treatment from Korean bathhouses and legal support from Wolfram & Hart. One the other hand, it was demons that serviced humans through their own special demonic talents such as Lorne's physic abilities, demon brothels which fueled certain men's fantasies and the demon Jenoff who granted humans their wish in exchange for their soul. Some demons offered power and wealth in exchange for live, human sacrifices.
Demons also seemed to have rather different views on beauty since the loose-skinned demon Clem found Buffy ugly because "her skin’s so tight I don’t know how you [Spike] look at her", Torg rejected Anya's offer of sex because he found her human appearance as unattractive despite once having a fling with her during her demon days and the inhabitants of Pylea found the half-demon Groosalugg's appearance to be monstrous and considered his human features as "defects" despite the Groosalugg being a physically attractive male by human standards, however, some demons have been shown to be attracted to humans like Syd Frzylcka who flirted with Winifred Burkle, Glory's Minions have called Glory's human counterpart Ben Wilkinson attractive, , a Chaos Demon with Drusilla, Krelvin with Carol Harris and the demonic prostitute Lina who was willing to service the vampire Angel so long as he didn't change into his vampire face. The demonic princess Jhiera also demonstrated a significant sensual interest for the vampire. Illyria sort out to seduce Connor, despite her moment of conception having passed.
The Slayer posed a sense of fear among demons, especially vampires. Demons would use the Slayer as a Boogeyman figure to scare their children into behaving. When Buffy led a group of powerless Potential Slayers into a demon bar for training, she claimed her presence was the only thing preventing the demons from attacking them.
Ironically, some demons considered the human beings as monsters to them. When Halloween was celebrated in the premises of Wolfram & Hart, the demon Devlin dressed himself as a human being (using real human skin to that effect), aping them excessively to the point it irritated the human-loving Lorne.
- “Demons cling to old ways and ancient feuds, but are hopeless with technology.”
When it came to modern technology, the majority of demons remained inept with most advances that humans possessed. Though some demons, mainly vampires, were conscientious of forms of media such as newspapers, televisions and electricity, they made very little use of modern weaponry and were usually limited to basic hand-to-hand combat and medieval weapons such as swords and axes.
On rare occasions, some made use of firearms. Examples of this behavior included Darla when fighting Buffy, Griff when collecting a dept, Lorne who killed Lindsey McDonald with a silenced pistol, M. James Menlo, prominent with firearm  and Razor, the leader of a demon biker gang who used a starting pistol when destroying the Buffybot.
It was unusual for a demon to use knives for disembowelment as they already had teeth and claws.
The demon Toth was considered a sophisticated demon for his use of mystical tools, such as the Ferula Gemini. Demons like Ken and Kathy Newman even knew how to use convincing prosthetic makeup.
Human Awareness of Demons
For most of history, the majority of humans remained unaware or in denial of the existence of demons, with notable exceptions including the Watchers Council, the Initiative, the Slayers, the Scooby Gang, the Angel Investigations team, and vampire hunters like Robin Wood, Sid, Daniel Holtz or Charles Gunn.
Rupert Giles explained this as the tendency for people to "rationalize what they can and forget what they can't." Aimee Mann, a guest singer at The Bronze, remarked that she hated playing in "vampire towns." To those who did know, demonic culture and mythology was the subject of scholarly research with ancient books and texts documenting their history. Having had knowledge of his real nature, Harriet, the ex-wife of Doyle became ethnodemonologist and had even become engaged to a demon. A website titled "Demons, Demons, Demons" also contained accurate information on demons. 
The Sunnydale High School board and the police department also appeared to be aware of the supernatural goings-on in Sunnydale, as the police often covered up vampire and demon attacks under orders from Richard Wilkins. When Spike and members of the Order of Aurelius attacked Sunnydale High to kill Buffy Summers, Principal Snyder and the police chief wrote it off to the public as an attack by a gang on PCP, an excuse that has apparently been used before.
In Los Angeles, it seems common that businessmen without scruples, gangsters or criminals, without counting the lawyers of Wolfram & Hart, are associated with demons in more or less doubtful business  .
In the early 21st century, the existence of vampires, and demons by extension, became public knowledge and vampires instantly became the subject of a fad, capitalizing on the fact that many humans experience a thrill when bitten by vampires. Harmony Kendall became the face of vampires in the media, starring in a reality show called Harmony Bites
Views of Demons
Humanity's views of demons, and their views of one another, vary considerably depending on individuals:
- Though the Scooby Gang and the Angel Investigations team were dedicated to destroying demons, they only sought to destroy evil ones. Both teams employed the services of demons on several occasions and many key members of both groups had been demons. In fact, the demon members of Angel Investigations often outnumbered the humans. Both also argued that werewolves should not be held accountable for their actions in bestial form as long as they found ways of restraining themselves. Regardless, both sides were perfectly willing and able to kill demons for committing bad deeds; for example, when Anya granted a wish that resulted in the deaths of several fraternity boys, Buffy immediately decided that she had to kill Anya for it despite having peacefully talked Dark Willow down after she did the same thing, justifying her actions by stating that Willow was human and Anya wasn't, and that as the Slayer, her decisions and judgement were absolute.
- Xander Harris has a deep hatred for all vampires, partly because of the death of his friend, Jesse McNally.
- Gib Cain hunted werewolves for their skin, uncaring that they were humans outside of the full moon.
- The Watchers Council refused to help Buffy Summers cure Angel of the Killer of the Dead poison on the grounds that he was a vampire, which resulted in her severing ties with the Council for over a year.
- On multiple occasions, the U.S. government and its different groups showed a desire to study supernatural beings and find a way to use their power for military purposes, the most prominent examples being the Initiative and the Demon Research Initiative, its World War II-era predecessor.
- Cordelia Chase initially believed that all demons, besides Angel, were evil until she discovered Allen Francis Doyle's Brachen demon heritage.
- One of the strains on the relationship between Buffy and Riley Finn was that he automatically assumed that all supernatural creatures were bad, harshly criticizing the Scoobies when he discovered that they had been harboring Spike, though he realized that demons were capable of both good and evil just as humans were when he helped save a werewolf, Oz, from the Initiative, especially after he witnessed his superiors' inhumane treatment of Oz while he was in human form.
- Mr. Maclay deceived both his late wife and his daughter Tara into believing that they were demons, allowing him greater control over them 
- M. James Menlo was considered a human criminal by the police. Because he was a specialist in explosives, it is possible that the authorities perceived him as a deformed human being.
- Gio, a rogue member of Gunn's Crew, led them on a fanatical crusade to destroy demons all over Los Angeles, regardless of their moral alignment.
- Anthony Harris' bigoted attitude toward Anya's demonic guests incited a riot between the two families. However, he was not aware of what they were really, considering them circus artists or a certain religious confession. It is plausible to say that he was simply reactionary by nature to all which is different from his own point of view.
List of Demons
- Demons had a tendancy to use the term 'clan' to refer to their own species as a whole. This could be seen with the Miquot Clan, the Ano-Movic Clan, the Tothric Clan, the Deathwok Clan, the Vinji, the Sahrvin Clan and the Goran Clan. It's likely that most demon species would only consist of a small population of members each due to their long lifespans and their predatory nature requiring them to remain in small numbers which may explain the use of the word 'clan'.
- It's odd that the demons of Pyleans characterize the Groosalugg's muscled arms as defects when demon champions like Landok also possesses a muscular physique. It's possible that due to demon's naturally possessing superhuman strength, it's only a rare occurrence in Pylea that a demon's muscles may develop as demons may generally not require training to know how to fight or hunt.