Kid Liberty was the teen sidekick to Captain Liberty in WWII. He went overseas in late ‘44 when the Axis broke the treaty regarding Meta-human combatants.
He returned home a hero and enjoyed celebrity.
He ran with the Rat Pack and it was Sinatra who gave him the name Yankee Doodle Dandy. Later just Yankee Doodle. Sinatra also insisted that YDD keep his mask on while in public because in his words, "I’m supposed to be the good lookin’ one."