"It all began in 1927. That's when Walt Disney's "Alice Comedies" cartoon series concluded - and when Disney signed a new contract with Universal Pictures. The plan was to create a new cartoon series under producers Charles Mintz and George Winkler. Disney and his colleague, head animator Ub Iwerks, devised a new character named Oswald the Lucky Rabbit."
The Walter Lantz Cartune Encyclopedia: Cartune Profiles: Oswald the Lucky Rabbit
Via Cartoon Brew