Ub Iwerks is well known for being the co-creator of the famous character Mickey Mouse, as he and Walt Disney co-created Mickey Mouse.
The first few Mickey Mouse and Silly Symphonies cartoons were animated almost entirely by Iwerks. However, as Iwerks began to draw more and more cartoons on a daily basis, he soon found himself unable to cope under Disney's harsh command. After a little while, Iwerks left the Disney company, and created his own animation studio, called The Iwerks Studio, but soon left and went back to Walt Disney Studios.