So, who's a quitter? Several people pointed out that Scott Adams (Dilbert) didn't quit, he was fired. (This is a great interview, sent in by Nancy, one of the longest I've ever read with anyone about anything). Actually, my opinion is that Scott quit conceptually, even though he kept showing up.
Others: Jeff Foxworthy, John Legend, Scott Clark, Gandhi, Tom Peters, Shea Gunther, Ernie Mosteller, Francis Crick, Bill Gates, Ray Kroc, Howard Stern, Francis Obikwelu, Dave Ramsey, Suze Orman, Harrison Ford, John Piper, Willem de Kooning, Jill Konrath, John Grisham, Jeff Bezos, Michael Bloomberg, Shawn Carter, Rowan Manahan, Ralph Roberts, Dan Schapiro, and even Apple, home of the Newton and the Apple III.
There were many more, but that ought to get you started.