Ragnaros

The being approaches you, sheathed in flame. Inside, you see what is plainly a humanoid figure, with two arms, two legs, a head, and eyes that glow with a bluewhite fire. The heat radiating from its body is intense, even at a distance. The air between you shimmers like the waves rising from the desert in the heat of deep summer...

Yeah, we killed him. Sure, it's two expansion packs later, but better late than never!