5. Nathan Fillion (Caleb)
Episodes: "Dirty Girls"; "Empty Places"; "Touched"; "End of Days"; "Chosen". Famous For: Slither; Serenity/Firefly; Castle etc. Nathan Fillion portrayed Caleb in five episodes of the fifth and final season of Buffy the Vampire Slayer. In the final season, the 'big bad' was the non-corporeal entity known as the First Evil - a being manifested from all evil in existence which can assume the intangible form of any dead person and an expert in psychological manipulation. Joss Whedon brought Caleb in as the First Evil's right hand man and main agent because, in Whedon's words, the First Evil's untouchable nature "meant that we didn't really have anything to push against. We needed... a sidekick. Somebody physical that we can see from episode to episode." He was a female-hating murderer who dressed as a priest to gain the trust of women and girls before killing them and it was this evil nature that attracted the First Evil to him. Caleb could merge with the First Evil and become strong enough to combat Buffy and her friends with ease. He killed a number of potential slayers and gouged out one of Xander's eyes. However, when Buffy got her hands on the slayer scythe - an ancient weapon meant to be wielded only by a slayer - she would ultimately defeat Caleb by using it to cut him in half. Fillion's likeness was also used in a brief appearance for Caleb in the season eight Buffy the Vampire Slayer comic books.