The central core of Pixar, when it originated at Lucasfilm, were people from NYIT led by Ed Catmull. John Lasseter didn't join until later, and he's the only prominent ex-Disney person I'm aware of.

It's a hell of a lot more complicated than that. The "founders" were not from Disney. John Lasseter who worked for the division that would be spun off from Lucasfilm was. But keep in mind for much of Pixar's life it was a hardware/software company producing tools for all kinds of high end imaging uses including animation. John Lasseter did cool demos and other projects to promote the hardware/software. The modern Pixar powerhouse of animation came to be more from accident/desperation than plan...