Mine would be Caleago. He was a Vampire hunting dwarf with living metal limbs and a face of pretty much all scar tissue. He seemed to have a very brutal backstory involving the flooding of his civilization via vampires in which he was the soul survivor, the near death experience that left him on a life debt for the vampire hunting guild, the murder of his wife, and his only child being turned into a vampire via ritual thus becoming his worst nightmare. Oh and to top it all off... he is a custom class where he gets powers from his ancestral viking background (basically a fighter who does a lot of fus-roh-da esc. powers) so of course he is a monster in his own eyes who could never raise a child anyway. so it goes bye bye to another dimension 100 years in the past. this is what he thought anyway. Turned out in the epilogue, the DM and I decided he was really completely insane and that he was the one who killed his entire race, was turned into a weapon by the guild, started laying waste to the land, kidnapped a random woman and murdered her, kidnapped a random child and threw it in a portal, burned down a temple and killed all the worshipers. and escaped to another land to start a new life (before hunting down every last god and demigod in existence to the point where another party member had to turn themselves into a god in order to destroy existence just before i nearly killed her too. (still the epilogue btw) but yeah... in terms of gameplay, somewhere between holding off a terasque single handedly, and throwing snowballs at enemy guards while hiding in a snowman deep within the high king's keep was just the most perfect thing ever. I think every session for about a year ended up being an inside joke with him.
