Buffy the Vampire Slayer features some fantastic villains over the course of its run, and the First Evil is by far the most powerful Big Bad with a very intimidating backstory and array of abilities at its disposal.
Many different forms of media tell unique vampire stories, but the work done with Joss Whedon’s Buffy the Vampire Slayer was transformative not just for the bloodthirsty undead, but for television’s ability to explore the horror genre and supernatural serialized storytelling. Buffy ran for seven seasons, launched a very successful spin-off, and has continued to see a healthy life in comic books. Buffy has covered a lot of territory, but the series’ villains are still incredibly memorable antagonists.
Buffy built a reputation with how each of its seasons would showcase a new Big Bad of increasing intensity. Buffy the Vampire Slayer has been able to tackle everything from ancient vampires, to government super soldiers, and even literal Gods, but Buffy season 7 goes even bigger for its swan song. The final season features the First Evil as its main antagonist, which tests Buffy and her gang more than ever before.
The First Evil is said to be the embodiment of all of the wickedness in the universe; it’s an ancient malevolent force that’s existed before the birth of the universe and will likely exist even after humanity has ended, since it’s impossible to just erase evil. The First Evil’s rise for power in Buffy the Vampire Slayer season 7 is triggered by Buffy’s second resurrection, which created an imbalance not only in the Slayer line, but also with the grander forces of good and evil. The First Evil seizes this opportunity to completely eliminate the concept of Slayers and, as a result, gain corporeal form or the ability to inhabit any living entity. The First Evil attacks in full force in season 7, but it first launched its plan back in Buffy the Vampire Slayer season 3, episode 10, "Amends". The First Evil takes the form of many of Angelus’ past victims, including Jenny Calendar, as a way to taunt Angel into killing Buffy or take his own life. The plan isn’t successful, but sets the precedent for the First Evil’s powers and scope when it returns.
The First Evil’s major strength is that it can take the form of anyone who’s died, which includes not only vampires, but also Buffy herself. The First Evil also gains the memories of those it mimics, which it allows it to masterfully manipulate and psychologically attack its prey. The First Evil can even plant brainwashing triggers in people’s minds, like what it temporarily does to Spike. Since the First Evil is non-corporeal, its biggest disadvantage is that it needs the help of others to do its bidding. This is seen with the Harbingers of Death, humans who the First Evil has corrupted and forced to commit rituals of self-mutilation. The First Evil also has control over the Turok-Han, a race of ancient vampires who are instrumental in the Battle at the Hellmouth. The First Evil uses Caleb, a murderous and deranged preacher, to lead these minions in their mission to eliminate the Slayers.
The First Evil is established to be eternal and cannot be completely destroyed. The key to its defeat is completely crippling it of its helpers and base of operations: the Hellmouth. The First Evil’s dark forces become quiet after Spike’s powerful amulet aids Buffy and company in their destruction of the Turok-Han and Harbingers. The Buffy video game, Buffy the Vampire Slayer: Chaos Bleeds, as well as the follow-up comics, make allusions to how the First Evil is dispersed across different dimensions; it will take centuries for it to be able to reassemble itself. While it’s not impossible that The First Evil could make a return as a Big Bad in Buffy the Vampire Slayer, its whole concept becomes weaker now that all Potential Slayers have been awakened.