Steamboat Willie was their first big hit. Other classic cartoon shorts that they made together include The Skeleton Dance, The Gallopin' Gaucho, The Barn Dance, The Opry House, The Plow Boy, The Karnival Kid, Haunted House, Springtime, Summer, and Autumn (what, no winter?), all of which made Walt Disney a household name. Ub Iwerks, meanwhile, decided he'd like to be his own boss, and with the help of producer Pat Powers, left Disney to go in business for himself.
Here's some of the delightful results from Iwerks brief (yes, I'm foreshadowing) stab at independence:
The Soup Song (1931)
The Air Race (1933)
Jack in the Beanstalk (1933)
Balloon Land (1935)
I find these, and many others that I've seen on YouTube, just as entertaining as anything Walt Disney, Max Fleischer or Walter Lantz (who had taken over Oswald) were doing at the time. But 1930s audiences were mainly indifferent, and Ub Iwerks never became a household word. However, he did retain a great deal of respect within the animation industry itself. Producer Leon Schlesinger, whose cartoons were distributed by Warner Brothers, farmed out some work to Iwerks. Schlesinger animators (and future directors) Robert Clampett and Chuck Jones assisted, and these bear more their stamp than Iwerks.
After producing some stuff for Columbia, Iwerks finally closed up shop in 1940 and returned to Disney. While he did some animation, he worked mostly on special effects, and later, even helped develop rides for Disneyland.
Before he died in 1971, Ub Iwerks did have one last hurrah that didn't involve Walt, or anybody you would normally associate with animation. But animation it was, though in order to tell you have to look closely...if you dare:
The Birds (1964)
Maybe Hitchcock should have asked Disney to lend him Donald Duck as well.