Lazurus!

Remember this one?

"The Alternative Factor" is a first season episode of Star Trek: The Original Series. It is episode #27, production #20, and was broadcast on March 30, 1967. The episode was written by Don Ingalls, and directed by Gerd Oswald.

In this episode, the crew of the Enterprise encounters a reality jumping madman. This is the first Star Trek episode to deal with parallel universes."