Older than humans and the Old Ones, the First Evil was an ancient power that preceded the written word, although it was younger than the Seed of Wonder. According to Beljoxa's Eye, who could see only the past and present, the First had existed long before the birth of the universe itself, and it would continue to exist even after there was nothing left of reality.

It was an incorporeal presence that could assume the form of any person who had died, including undead vampires and those who had been resurrected. Because of this, it appeared in various forms depending who it sought to manipulate. The appearance it used to portray itself was seemingly in the form of a large robed beast.

During Christmas 1998, the First appeared in Sunnydale. It tried to drive the ensouled vampire Angel into killing the Slayer Buffy Summers, by appearing to him as some of the people he had murdered. The First told Angel that it was responsible for his return from Acathla's dimension and that he could end his sufferings by giving in to his inner demon. Angel was eventually able to resist the First, effectively rendered it powerless.

Buffy's death and resurrection in late 2001 disrupted the mystical forces surrounding the Slayer. So, in the following year, the First Evil began its attempt to use this as a catalyst to destroy the Slayer line, which would allow the primordial entity to take over the world and gain corporeal form. This involved assigning his followers, the Harbingers of Death, to track down and eliminate all Potential Slayers, before turning their attention towards Buffy and Faith, thus destroying the line completely.

Buffy and her allies were able to defeat its army effectively rendered it powerless once more.