SWTOR, the final boss for the planet quest on Voss. He was called the avatar of Seh-Run I think. If you didn't have an interrupt (which at the time I fought him on my merc I didn't) he would one-shot you. I think I tried it at least 15 times (each with about a 5 minute travel time) before I got a guildy to come help me. I still have nightmares...

