In Luthor's earliest appearances, he is shown as a middle-aged man with a full head of red hair. Less than a year later however, an artistic mistake resulted in Luthor being depicted as completely bald in a newspaper strip. The original error is attributed to Leo Nowak, a studio artist who illustrated for the Superman dailies during this period. One hypothesis is that Nowak mistook Luthor for the Ultra-Humanite, a recurring mad scientist foe of Superman who, in his Golden Age incarnation, resembled a balding, elderly man. Other evidence suggests Luthor's design was confused with that of a stockier, bald henchman in Superman #4 (Spring 1940); Luthor's next appearance occurs in Superman #10 (May 1941), in which Nowak depicted him as significantly heavier, with visible jowls. The character's abrupt hair loss has been made reference to several times over the course of his history. In 1960, writer Jerry Siegel altered Luthor's backstory to incorporate his hair loss into his origin.