Illyria

Illyria (reborn 2004 in Los Angeles) was one of the Old Ones, the powerful pure-breed demons which ruled earth prior to and during the rise of mankind. In 2004 she reincarnated in the body of Winifred Burkle.

Millions of years ago
Illyria was one of the thousands of Old Ones that plagued the world when mankind was still evolving, and was one of the most feared and worshipped. She ruled over the area of modern California from her temple Vahla ha'nesh and commanded an army composed by thousands of demons, which she used to constantly make war on her rivals. However, Illyria was eventually murdered by her rivals and placed in a stone sarcophagus to prevent her resurrection. When the Old Ones were driven away from this world, the coffins containing the remains of the fallen Old Ones were placed in the Deeper Well.

However, prior to her death, Illyria crafted a plan to resurrect millions of years later and raise her army to recuperate her status of power. Illyria's army was locked in Vahla ha'nesh and the temple was put out of phase with our timestream in order to keep it hidden. By unknown means, Illyria's sarcophagus would teleport itself back to California, where her Qwa Ha Xahn, her high priest, would resurrect her.

Present
Illyria's resurrection was masterminded by her worshipper Knox, who chose Fred, whom he had fallen in love with, as the vessel for Illyria's reincarnation. However, due to geological changes and the continents shifting from place, the sarcophagus teleported outside of the United States. Somehow it gon transported to U.S. soil, but was held up at Customs at LAX airport. Knox plotted with Doctor Sparrow, who blackmailed Charles Gunn into using his restored knowledge of the laws to release the sarcophagus from Customs.

After its release, Knox had the sarcophagus delivered directly to Fred at Wolfram & Hart's science lab. In order to keep his cover, Knox claims that the sarcophagus is impenetrable to lasers and imaging beams. When Fred touches one of the purple crystals embedded into the surface of the coffin, a gust of air (Illyria's essence) is released directly to her mouth. Instead of merely possessing Fred, Illyria manifests as an infection that liquifies her organs, hardens her skin and (allegedly) consumes her spirit. After hours of increasing agony, Fred's body is completely taken over.

Powers
The full scope of Illyria's power is unknown. When Illyria takes over her new "shell", she has tremendous physical strength. Spike likens a blow from her to being hit by a Mack truck. Her strength, reflexes, and agility make her a formidable hand-to-hand combatant. She uses an ancient fighting style that Spike compares to Tae Kwon Do and "Brazilian Ninjitsu" (probably Capoeira). Although Spike's adaptability gives him an occasional advantage, Illyria generally dominates their sparring sessions. Her skin is a hardened shell, providing her body with a heavy armor capable of withstanding blows from forged weapons (e.g. swords or axes). She is aided in combat by her ability to selectively alter time, which allows her to easily dodge both attacks and bullets; she can accomplish a goal and leave an area before her opponent even realizes she has moved. She can also open interdimensional portals. In the episode titled "Underneath", Wesley comments on her not needing to sleep. She can alter her physical appereance on a basic level, and she is capable of recreating Fred's persona accurately enough to fool Fred's parents. She tells Knox that she can take any form she chooses. Her senses are enhanced, which enables her to recognize that Connor's body warms when he sees her, indicating his lust. She communicates with flora, often spending hours at a time communing with a plant. Illyria is also capable of distinguishing humans (or "primitives"), from demons, vampires and other half-breeds. For example, she perceives that Marcus Hamilton is neither human nor demon (referring to him as a "creature"). She also retains the insights from her experiences as an Old One, which enable her to effectively analyze the power dynamics, personal motivations, and emotions that influence those around her.