A gaming term that derived from any multiplayer "shooter" video game where "elimination" is involved. A "hero" is the last standing player who successfully completes the round through major extremities or when the odds are stacked heavily against them.
Call of Duty; Search & Destroy: "He was the only one on our team alive and he took down 5 (or all 6) guys by himself and won the round. He's a 'Hero'.
Gears of War; Horde mode:
"'Hero'! He completed the wave (there has to be a significant amount of locust alive, of course) on his own after we all died."
*The key thing to remember is that this person (or hero) has to be ALONE when the odds are stacked SIGNIFICANTLY against him (for Search & Destroy, at least 5 guys); yet he still eliminates the opposition AND wins the round.