Fake Shemp - Body doubles used in movies to replace actors who die or are otherwise unavailable

Coined by film director Sam Raimi, the term is named after Shemp Howard of The Three Stooges, whose sudden death in 1955 necessitated the use of these techniques to finish the films to which he was already committed.

adding to my mental list of Raimi facts

I thought I recognized a still from Plan 9 From Outer Space, by Ed Wood.