with censors. Siegel was forced to tone down the violence and social crusading that characterized his early stories. Editor Whitney Ellsworth, hired in 1940, dictated that Superman not kill. Sexuality was banned, and colorfully outlandish villains such as Ultra-Humanite and Toyman were thought to be less nightmarish for young readers. Mort Weisinger was the editor on Superman comics from 1941 to 1970, his tenure briefly interrupted by military service. Siegel and his fellow writers had developed the character with little thought of building a coherent mythology, but as the number of Superman titles and the pool of writers grew, Weisinger demanded a more disciplined approach. Weisinger assigned story ideas, and the logic of Superman's powers, his origin, the locales, and his relationships with his growing cast of supporting characters were carefully planned. Elements such as Bizarro, his cousin Supergirl, the Phantom Zone, the Fortress of Solitude, alternate varieties of kryptonite, robot doppelgangers, and Krypto were introduced during this era. The complicated universe built under Weisinger was beguiling to devoted readers but alienating to casuals. Weisinger favored lighthearted stories over serious drama, and avoided sensitive subjects such as the Vietnam War and the American civil rights movement because he feared his right-wing views would alienate his left-leaning writers and readers. Weisinger also introduced letters columns in 1958 to encourage feedback and build intimacy with readers. Weisinger retired in 1970 and Julius Schwartz took over. By his own admission, Weisinger had grown out of touch with newer readers. Schwartz updated Superman by making Clark Kent a television anchor, and he retired overused plot elements such as kryptonite and robot doppelgangers. Schwartz also scaled Superman's powers down to a level closer to Siegel's original. These changes would eventually be reversed by later writers. Schwartz allowed stories with serious drama such as "For the Man Who Has Everything" (Superman Annual #11), in which the villain Mongul torments Superman with an illusion of happy family life on a living Krypton. Schwartz retired from DC Comics in 1986 and was succeeded by Mike Carlin as an editor on Superman comics. His retirement coincided with DC Comics' decision to reboot the DC Universe with the companywide-crossover storyline "Crisis on Infinite Earths". Writer John Byrne rewrote the Superman mythos, again reducing Superman's powers, which writers had slowly re-strengthened, and revised many supporting characters, such as making Lex Luthor a billionaire industrialist rather than a mad scientist, and making