Richard Branson had partners when we started Virgin Records. After Virgin Records, he had enough money to hire for all his other businesses right off the bat. Felix Dennis was solo, and strongly believes in holding on to as much equity as possible, but if you read his book, he'll tell you what a miserable time it was. (He often wished he was dead.)

I've bootstrapped a business to significant traction as a single founder. I don't recommend it. It's possible, but morally exhaustive.

Larry Ellison had two co-founders. I believe that both of them left the company in the early '90s.