Who hosted the tonight show before leno and after Carson?

Johnny Carson never did "reruns" of his shows; every show was new and fresh. Carson took plenty of vacations, but whenever he was away, one of a number of "guest hosts" would take the big seat. Jay Leno was one; Don Rickles and actress Joan Rivers were others. When Carson announced his impending retirement, NBC tried a number of different people who had guest-hosted The Tonight Show, and settled on Leno pretty quickly.

So the straight answer would be "There were no permanent hosts of the Tonight Show between Carson and Leno."

My complaint with Leno is that when he took over, he "pulled up the ladder behind him", and never allowed anybody else to guest-host the show, and never allowed new talent a chance to develop their own styles. Like a professor who refused to teach, he tried - intentionally or not - to block any competition from developing.