https://memory-alpha.fandom.com/wiki/Spock_(mirror)
Mirror,_Mirror is quite an interesting 1967 Star+Trek episode.
https://memory-alpha.fandom.com/wiki/Mirror,_Mirror_(episode)
https://memory-beta.fandom.com/wiki/Mirror,_Mirror
https://memory-beta.fandom.com/wiki/Spock_(mirror)
The Spock and the alternate Spock.
https://en.wikipedia.org/wiki/Parallel_universes_in_fiction#Multiple_worlds_and_time_travel
https://en.wikipedia.org/wiki/Parallel_universes_in_fiction#Simulated_reality
Of course it wasn't just in Star+Trek that Leonard_Nimoy played a character in an Alternate_Universe.
https://fringe.fandom.com/wiki/William_Bell#Season_One
https://fringe.fandom.com/wiki/There's_More_Than_One_of_Everything#Plot
