In "Dark Knight Over Metropolis" (Action Comics #654), Batman discovers a Kryptonite ring created by Lex Luthor. He turns it over to the Man of Steel, but Superman returns it to Batman saying, "I want the means to stop me to be in the hands of a man I can trust with my life."
The Ultra-Humanite was the first super villain Superman ever faced. He first appeared in Action Comics #13 and was designed to be the polar opposite of Superman: while Superman is a hero with superhuman strength, Ultra-Humanite is a criminal mastermind who has a crippled body but a highly advanced intellect.
In the Bottle City of Kandor, Superman had no powers and was branded an outlaw due to a misunderstanding. To protect themselves, Superman and Jimmy Olsen created vigilante identities inspired by Batman and Robin; however, as neither bats nor robins existed on Krypton, Superman chose the names of two native avian species: Nightwing (for himself) and Flamebird (for Jimmy).
Titano first appeared in Superman #127 (February 1959). A common chimpanzee who was rocketed into space, he and his ship were bombarded with radiation, which changed him into a giant ape with incredible strength and the ability to emit beams of Kryptonite radiation from his eyes.
Superman has long been seen as a patriotic symbol of "truth, justice, and the American way," from his embrace of traditional American ideals to the iconic red and blue of his costume, but in Action Comics #900 he renounces his U.S. Citizenship and vows to continue working as a superhero from a more global perspective.