Steve Wilson was a veteran from the U.S Army who fought in the war years of 1948 when America was being attacked by a Nazi organization called the Cerberus Faction, lead by their leader the Black Skull. To defeat the Cerberus Faction, the Chief became a super soldier after the U.S Army placed him into a machine.
This machine gave Chief U.S a muscular body which was both bullet proof, and gave him a ton of combat skills to fight off against the Cerberus Faction. After losing his best friend, and defeating the Black Skull, Chief U.S froze himself for half of a century, until he was found by the other future Saviors today. Now you see the Chief standing next to the jet. "Glad you could come, and assist, but who's the boy?" the Chief asks. "Just someone that needs protection," the Metal answers.