Mickey Mouse

After having lost the rights to Oswald, Disney had to develop a new "star". Most Disney biographies state that Disney came up with a mouse character on his trip back from New York. It is debated whether it was he, or Iwerks who actually designed the mouse (which basically looked like Oswald, but with round instead of long ears). Another explanation is that this was simply the drawing style of animated characters back then, and that Iwerks adopted it. Besides Oswald and Mickey, this can be seen in the Alice Comedies which featured a mouse named Ike the Mouse, and in the first Flip the Frog cartoon called Fiddlesticks, showing a Mickey Mouse looking mouse playing fiddle. The first films were animated by Iwerks, his name was prominently featured on the title cards. The mouse was originally named "Mortimer", but later christened "Mickey Mouse" by Lillian Disney who thought that the name Mortimer did not fit.
Mickey's first animated short produced was Plane Crazy, which was, like all of Disney's previous works, a silent film. After failing to find distributor interest in Plane Crazy or its follow-up, The Gallopin' Gaucho, Disney created a Mickey cartoon with sound called Steamboat Willie. A businessman named Pat Powers provided Disney with both distribution and Cinephone, a sound-synchronization process. Steamboat Willie became a success, and Plane Crazy, The Galloping Gaucho, and all future Mickey cartoons were released with soundtracks. Disney himself provided the vocal effects for the earliest cartoons and performed as the voice of Mickey Mouse until 1946. After Steamboat Willie was released, Mickey became a very close competitor to Felix the Cat, and Walt Disney would continue to successfully use sound in all of his future cartoons as well. Upon the failure of Felix the Cat's transition to sound in 1930, Mickey Mouse became the world's new favorite animation character.