Game: The Diablo series (1996-2012)

He's the Devil, what more needs to be said? Well, actually, he's a devil but as the most feared evil in Blizzard's series, Diablo takes the cake and sets it on fire. As PC games go, this boss stands above all others. He has the ability to control hellfire, call monsters to do his bidding and hurl gamers into dark dimensions mid-battle. Battling this boss cost a ton of red potions in order to survive. This evil creature has become iconic despite changing design in each game.