- “We're so far beyond you. Beyond what you can even imagine.”
Nash and his sister Pearl were powerful half-demons who were in the service of Twilight. Their mother was a human who intentionally bred with a demon, believing that their children represented the "next stage of evolution." Trying to impress their master, the two of them massacred an entire Slayer squad with the exception of Nadira. After the downfall of Twilight, Pearl and Nash were recruited by Whistler to take vengeance on Angel and to somehow "save the world" and bring forth the next step of evolution.
In 1935, Nash, along with Pearl was born to a human, who intentionally bred with a demon, believing her children to be the next step in evolution. In 1940, at the age of five, they were schooled regularly by their mother about their "greater purpose" and taught to uphold and live up to it the best way they could.
In 1970, Pearl and Nash both followed their mother's plan and bred with demons themselves. All of their children were killed by monster-hunters however, among then Alasdair Coames. Their mother then suggested to them that instead of breeding with demons, they breed with humans posessing strong magic, since not being able to blend in made their children vulnerable.
At some point, Nash proposed marriage to Lavinia and Sophronia Fairweather to make them his dual-brides, but they stole his engagement ring, the Ring of Narcissius, and left.
Working for "Twilight"
Many years later, Pearl and Nash were approached by Twilight who told them of his plans to create a new, evolved universe, which along with his promise of bloodshed made them agree to work for him. Under his leadership, they killed Nadira's squad of slayers.
After Angel renegaded on the Twilight affair, Pearl and Nash vowed revenge against him. After the loss of magic, their mother was no longer able to prolong her life and asked her children to kill her. After they had massacred all the patrons of a bar, Whistler informs them that the world which doesn't know it's dead yet, needs to evolve. The twin accepted Whistler's proposition for the sake of bringing in the next stage of evolution and getting payback on their old boss, something their mother supported.
Working for Whistler
Attempting to find Angel, the three demons tracked him to Rupert Giles's former apartment- where Angel now lived with the slayer Faith Lehane as he attempted to complete Giles's unfinished business and find a way to bring the now-dead Giles back to life-, but only discovered Giles's aunts, Lavinia and Sophronia Fairweather that Nash know since many times after both sisters refuse his wedding proposition, as Angel was currently in Quor'toth with Faith, Willow Rosenberg and Connor. Informing the Giles family that he intended to complete the ascension that Buffy and Angel had interrupted as part of a plan to save the world by evolving it to the next stage, Whistler gave the aunts a card with an address on it and told them to tell Angel to meet him there on their 'anniversary'.
Later, the three demons concludes a pact with a very-living Eyghon the Sleepwalker to try and restore magic using accumulated magical artefacts to trigger a magic 'plague', with Whistler agreeing to give Eyghon control of Europe after magic has been restored, to rule as he sees fit. However Eyghon doesn't trust for Pearl and Nash, conscious and afraid that they don't want share the power and try to double-cross him.
When Alasdair's "cloaking device" for his magical items was shut down in an effort to help resurrect Giles, Whistler and his group quickly arrived on the scene. Pearl and Nash fiercely fought with Angel and Faith, intending to steal the items necessary. Eventually, when the three managed to steal the items, Whistler ordered the two of them to retreat since they had gotten what they wanted. Reluctantly, they obeyed and Whistler left again with them on his mission. 
Miraculously, Giles was successfully resurrected, but as an adult in a twelve-year-old body. With Giles' urging, Angel and the others headed out to stop Whistler's plan with the mutual agreement that not all of them would survive the fight. In the ensuing confrontation on a rooftop in Hackney, London, Angel desperately attempted to reason with Whistler, not wanting to fight his friend and benefactor, but his pleas fell on deaf ears; still believing that he was saving the world, Whistler unleashed a magical plague, mutating several people into monsters.
After aligning himself with Whistler in an attempt to exact vengeance on Angel and fulfill his part in evolution, Nash would later be stabbed in the back by a fatally burned Nadira and then killed by Faith afterwards, leaving Pearl alone.
Nash demonstrated a blatant lack of empathy and disregard for human life, not for same reasons that most demons did. Because of his half-demon status, he felt human emotion when losing his mother, was very protective to his twin sister. This combination made him a particulary dangerous and unpredictable demon. Indoctrinated by his mother, he considered himself superior to humans that he determined weak and viewed other demons, save for Whistler, archaic. In the past, he was also very romantic, flirtatious with the Fairweather sisters.
Nash resembles a human man, however with a snub nose, bright azure eyes, and exaggeratedly pointed ears.
He possesses a very long lifespan and matching decelerated aging process; having been born around 1936, and being a young child at 1940, he was still at his physical prime at the beginning of the 21th century. He can also fly, project green energy beams from his eyes, generate energy weapons and drew strength from primal emotions (hate, fear, pain, etc.).
Behind the Scenes
- Artist Rebekah Isaacs partly modeled Nash's appearance on David Bowie's "Thin White Duke" persona. This was referenced in Angel & Faith #21, when Faith calls Nash "David Bowie".
- After Billy Blim and Darrow Steele, Nash is the third half-demon to be killed because a woman attacks him from behind, which he would probably have killed her easily in a fair two-man fight.
- "Live Through This, Part One"
- "Live Through This, Part Two"
- "Live Through This, Part Three"
- "Live Through This, Part Four"
- "Family Reunion, Part One"(Only mentioned)
- "Family Reunion, Part Two"
- "Family Reunion, Part Three"
- "The Hero of His Own Story" (Also in flashbacks)
- "Death and Consequences, Part Three" (in flashbacks)
- "What You Want, Not What You Need, Part One"
- "What You Want, Not What You Need, Part Two"
- "What You Want, Not What You Need, Part Three"
- "What You Want, Not What You Need, Part Four" (killed)
- "Where The River Meets The Sea, Part Four" (Only mentioned)