In the forties, when Wonder Woman came to the "mans world", she wanted to be near Steve Trevor. She met Diana Prince, a nurse at the hospital Trevor was in. Prince wanted to go to her fiancee who moved to South America, but couldn`t, because the couple didn`t have enough money for Prince's plane ticket.
Wonder Woman paid her in exchange for her identity. She went off to lead her life Wonder woman had a secret identity.
Later, the first Diana Prince returned to reclaim her previous identity. But, due to some troubles with Nazis, she decided to leave again. She got a new identity: Diana White.