An alien from "a far off planet" whose father, Vyl, died in a space prison some time after his arrest at the hands of Superman and Batman. Honoring Vyl's death-bed wish, Xan launches a campaign of revenge against the two Earth heroes in August 1967, resurrecting the Composite Superman, the only villain to have beaten them before ("Before I destroy them, I want them to suffer!"). As the Composite Superman defeats the heroes and is on the verge of killing them, Xan removes the villain's powers and returns him to his identity as Joe Meach in a bid to kill Superman and Batman himself with a "Magna-Gun" of his own invention. The attempt is foiled when Meach takes the blast himself in a final act of self-sacrifice. The heroes subdue Xan, who is "incarcerated on his own world." (WF No. 168: "The Return of the Composite Superman!", pt II; "The Half-And-Half Heroes!")
Many years later, Xan returns and takes on the Composite Superman powers himself, calling himself Amalgamax. Superman and Batman enlist the help of the Legion of Super Heroes to stop him (WF No. 283, Sep 1982: "Prologue"; WF No. 284, Oct 1982: "I - Amalgamax").