In 1930, Iwerks opened "The Iwerks Studio" after feeling overworked and under appreciated by Walt Disney. Pat Powers, who had originally sold Disney their first Cinephone system, recognized that Iwerks was a main contributor to Disney's success and made a deal that would let him produce his own animated shorts. With a deal from MGM, Iwerks made shorts featuring the characters "Flip the Frog" and "Willie Whopper," although these shorts were never nearly successful enough to compete with either Disney or Fleischer Studios. In "Fiddlesticks," made in 1930, it is clear that he is making reference to his time at Disney with a character that closely resembles Mickey (his co-creation!):
From 1933 through 1936, Iwerks worked on independently distributed shorts in Cinecolor, called ComiColor Cartoons. Here is the really wonderful "Balloon Land" from 1935:
Finally, when he returned to work for Walt Disney Studios after little success on his own, he was put in charge of developing special visual effects, in which he is credited as developing the process which combines live action and animation, used the feature "Song of the South" from 1946:
Iwerks also not only contributed to the development of many of the Disneyland attractions, but also did Academy Award nominated special effects for Alfred Hitchcock's "The Birds." Ub Iwerks is really great and has always deserved more credit than he's received.