Jack Lord was the first choice to play Captain Kirk on Star Trek
George Lindsey and Martin Landau both turned down the role of Spock
When Martin Landau left Mission Impossible, He was replaced by Leonard Nimoy. The guest star on Nimoy's first episode was William Shatner.
As long as people talk about you, you're not really dead. As long as they speak your name, you continue. A legend doesn't die just because the man does.