"I never fear violence. 'Cause I'm no coward!" —U.S. Agent U.S. Agent, a.k.a. John Walker, is a character from Marvel's The Avengers who appears as a playable secret character in Marvel Super Heroes vs. Street Fighter and as an assist character in Marvel vs. Capcom: Clash of Super Heroes. Although he is a different character in the comics, he is a palette swap of fellow Avenger Captain America in the games.