Doombringer is a powerarmored assassin, sort of a Mech-assassin on steroids, but I was using him long before Mech-Assassin was introduced.
His armor is virtualy indestructable and gives him enhaced characteristics and movement. He primary offensive powers come from his Variable- Special effect weapon system that allows him to pull virtualy any type of attack to bear on his opponents.
I do not make a habit of killing the heroes of my campaign, but Doombringer has in fact killed at least 1 character of each of my players at one time or another.
Credit for inspriation for Doombringer goes to Marvel comics who used a one-time villain named Doombringer in a PowerMan and Iron Fist comic. I liked the name, and designed my own version for my campaign.