Superman, given the serial nature of comic publishing and the length of the character's existence, has evolved as a character as his adventures have increased. The details of Superman's origin, relationships and abilities changed significantly during the course of the character's publication, from what is considered the Golden Age of Comic Books through the Modern Age
The powers and villains were developed through the 1940s, with Superman developing the ability to fly, and costumed villains introduced from 1941. The character was shown as learning of the existence of Krypton in 1949. The concept itself had originally been established to the reader in 1939, in the Superman comic strip.