In Earth X, Jack of Hearts was initially one of many heroes and villains subjugated by the mental domination of the Skull. Once his mind was freed, Jack traveled to the U.K. and became a knight in the service of King Britain. He fought for his king several times, against Mephisto, the Deviants and the Tong of Creel. Jack also earned the affections of Luna of the Inhumans.
Jack was first depicted as an Avenger in Avengers Forever, part of an alternate future squad including Wasp, Thor, Justice, Quicksilver, Songbird and Genis-Vell as Captain Marvel. They operated from the traditional mansion and had finished battling Oort and his Solar Squadron when Songbird was whisked away for the Destiny War.