One of Walt Disney’s oldest friends was sure Ub Iwerks. He has been with Walt since the earliest days of his career and played a very important role in the creation of Mickey Mouse. But in 1930 Ub Iwerks, after almost a decade spent working with Disney, left Walt’s studio to form one of his own. The first cartoon produced there was "Fiddlesticks", produced in Two-strip Technicolor. It's a cartoon like many others from the early 1930s, without an actual plot, but made of musical numbers where the characters sing and dance along with the music. The star of the cartoon, Flip the Frog, who appeared in 38 Ub Iwerks cartoons between 1930 and 1933, was created by Iwerks at the Disney studio, when he was still working there: an early version of the character appeared in the Silly Symphony “Summer”.
The influence of the Disney days in Iwerks' early solo work is clear: for example, in "Fiddlesticks", Flip's fiddle-playing pal bears a strong resemblance to a certain well-known mouse. It is debatable, though, whether Iwerks could be considered or not the real "man behind the mouse"; in fact, Disney never drew any of Mickey’s cartoons, which were completely animated by Iwerks during the early years. If you ask me, he actually was Mickey's creator.
Anyway, here you can see some pictures from Flip's debut in "Fiddlesticks":