Main article: Mickey Mouse
After losing the rights to Oswald, Disney felt the need to develop a new character to replace him. He based the character on a mouse he had adopted as a pet while working in a Kansas City studio.[36] Ub Iwerks reworked on the sketches made by Disney so that it was easier to animate it. However, Mickey's voice and personality was provided by Disney. In the words of a Disney employee, "Ub designed Mickey's physical appearance, but Walt gave him his soul."[36] Besides Oswald and Mickey, a similar mouse-character is seen in Alice Comedies which featured a mouse named Ike the Mouse, and the first Flip the Frog cartoon called Fiddlesticks, which showed a Mickey Mouse look-alike playing fiddle. The initial 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. Mortimer later became the name of Mickey's rival for Minnie, who was taller than his renowned adversary and had a Brooklyn accent.

The first animated short with Mickey in it was titled, Plane Crazy, which was, like all of Disney's previous works, a silent film. After failing to find a distributor for 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 an instant success,[37] 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 the release of Steamboat Willie, Walt Disney would continue to successfully use sound in all of his future cartoons, and Cinephone became the new distributor for Disney's early sound cartoons as well.[38] Mickey soon eclipsed Felix the Cat as the world's most popular cartoon character.[36] By 1930, Felix, now in sound, had faded from the screen, as his sound cartoons failed to gain attention.[39] Mickey's popularity would now skyrocket in the early 1930s.[36]