While the rest of Disney’s studio was toiling away on the last few “Oswald the Lucky Rabbit” shorts that they were contractually obligated to finish for Universal, Ub animated the first Mickey Mouse cartoon, Plane Crazy, alone and in complete secrecy. During work hours, Ub would place dummy drawings of Oswald on top of his Mickey drawings so nobody would know what he was doing. At night, Ub would stay late and animate on Mickey. He animated the entire six-minute short singlehandedly in just a few weeks, reportedly averaging between 600-700 drawings a night, an astounding feat that hasn’t been matched since. When the success of Mickey Mouse propelled the Disney studio to new heights, Ub continued his efficient streak by animating extensive footage on Silly Symphonies shorts like The Skeleton Dance and Hell’s Bells.

He was responsible for the distinctive style of the earliest Disney animated cartoons, and was also responsible for creating Mickey Mouse. In 1922, when Walt began his Laugh-O-Gram cartoon series, Iwerks joined him as chief animator. The studio went bankrupt, however, and in 1923 Iwerks followed Disney’s move to Los Angeles to work on a new series of cartoons known as “the Alice Comedies” which had live action mixed with animation. After the end of this series, Disney asked Iwerks to come up with a new character. The first Oswald the Lucky Rabbit was animated entirely by Ub Iwerks. Following the first cartoon, Oswald was redesigned on the insistence of Universal, who agreed to distribute the new series of cartoons in 1927.