Steve Trevor is a USAF pilot, and romantic interest to Wonder Woman. During a mission, he crash-landed and accidentally discovered the island of Paradise Island, home of the Amazons.
During the Silver Age, Steve was killed early on, and replaced by Steve Howard, which was actually Eros' spirit in the dead Steve's body. After he too died, a third Steve appeared, who came from another universe (Earth-270). They were eventually merged into one by Aphrodite.
Steve Trevor was created by William Moulton Marston and Harry G. Peter, first appearing in All-Star Comics #8. (1942)