Fultheim the Fearless is one of three hostages during the quest "With Friends Like These...." He is a mercenary who was captured from a battlefield. He does not have any ill thoughts against anyone but many people would definitely put a contract on him due to his occupation that involves killing many people, the relatives of the victims may have a grudge against him.
He is one of three possible murder victims after the Dragonborn is abducted by Astrid and brought to the Abandoned Shack. If Fultheim is killed, Astrid congratulates the Dragonborn with, "Oh ho. The whimpering Nord, eh? Yes, yes, I can see how you'd come to that conclusion. Interesting choice."
Despite his name and occupation, Fultheim is quite cowardly. He constantly fights back tears and begs for mercy while you interrogate him.