If you love the old Mickey Mouse silent cartoons such as Plane Crazy, you really love Ub Iwerks and not Walt Disney. While Disney owned and operated his studio, and sometimes directed the cartoons he produced, he had little artistic talent and that is where Ub Iwerks came in. A talented and prolific artist, he could turn out as many as 700 drawings in one day, about 10x the average output, frequently animating an entire cartoon by himself. He also was a visionary in plots and execution and is largely responsible for Disney's early success.
But in 1930, money and credit for intellectual property came between them and Ub left to form his own studio. He was forced to sell his Disney stock, which, if left intact, would have been worth many billions today. But the cartoons he produced were excellent, as seen in the embed. You'll notice how suspiciously the mouse antagonist resembles another mouse of the time.
Ub's studio produced many color cartoons which were well-received, but the competition was simply too great and he did not have to resources to enjoin his other studio competitors. Eventually, Ub's studio failed and he was forced to return, hat in hand, to Disney, who did rehire him but he was never again in a position of any power. Walt Disney had the upper hand and used it shamefully. At the end, Ub was a broke and broken old man and his last hurrah at Disney was to produce the animated sequences in 1964's Mary Poppins.