https://youtu.be/kCZPzHg0h80
After the initial success of Mickey Mouse, Ub and Walt had a falling out, and Iwerks headed his own cartoon studio for a time in the 1930’s. Ub eventually returned to Disney, where he was a technical innovator.
The complete podcast about Ub Iwerks is at this link. It’s worth noting that Ub isn’t an obscure figure to anyone with more than a passing interest in animation.