First Appearance: Captain America v1 #17 (August 1942).
Golden Age Appearances: Captain America v1 #17.
Modern Appearances: USAgent #3 (referred to, believe it or not).
Years Active: 1941-?
The Fighting Yank is Bill Prince, an operative of the American government in China helping the Chinese fight against the invading Japanese. He has no superpowers but is a good fighter.
Note: The Fighting Yank, of all characters, is seen on a list of patriotic heroes in USAgent #3, thus firmly placing him in modern Marvel continuity. Hard to believe, but there it is.