@EHeroAndrew Its been almost forty years but it was a prehistoric creature who was hibernating in a lake in the Forbidden Zone and a piece of road gravel from one of the Ape's army jeeps' tires was flung into the lake, beaned the creature on the head(I'm serious) and woke it up.
Why didn't they use the original actors to voice the characters: Roddy McDowell, Nathalie Trudy, Marice Evans, Kim Hunter, Linda Harrison, and Claude Atkins.