Character Snapshot: Angelus is the soulless counterpart of the redeemed vampire named Angel, who when in possession of a soul, is actually a well-meaning, albeit brooding, hero.
The Story: Angel is a good vampire, and he and Buffy are in love. But when they have The Sex, that moment of bliss triggers an old curse on Angel. His soul is snatched away from him and he reverts back to a soulless vampire.
"I want to torture you. I used to love it, and it's been a long time. I mean, the last time I tortured somebody, they didn't even have chainsaws."
Why They Scare Me: Angelus was a shocking character because his arrival was abrupt and a complete 180 from the Angel we knew. He wasn't possessed, he was just... Angel without a soul. And it was scary. I personally think David Boreanaz never acted better than when playing Angelus (especially modern day!Angelus, because flashback!Angelus had that accent, lol). The character loved to play mind games and had ~200 years of experience. Over the course of season 2 of BtV, Buffy had to deal with not only losing her boyfriend, but gaining a sadistic villain who took glee from taunting her and fucking with her and was so, so good at it.
Buffy did make hard choices and got rid of Angelus... for the time being. Angelus made a reappearence in season 4 of AtS, when the gang needed him in order to gleam important deets on the new Big Bad. Even when stuck behind bars, he taunted his friends and his son with details he knew about them all, turning them against each other. I'm pretty sure he got out of the cage, too, but my memory of that is hazy, lol.
Scariest moment: Snapping Jenny's neck and lovingly displaying her body for Giles to find.
Runner-up in Buffy-verse: Probably Caleb of BtV season 7. That thing with Xander's eye, omg! D:
Hint for tomorrow's Scary Character: "My investigations have begun."
Caps from leavemethewhite.com and Angel Screencaps.