He was the prime mover of Star Trek II: Wrath of Khan, and then the II, III and IV Spock Dies and returns to save the whales "arc."
It may not be an exaggeration to say he saved the franchise's continuity and maybe the franchise itself.
I think he did a cameo as the "Admiral" talking Kirk into taking on a mission, later on. Can't place the precise moment, maybe V.
Yes, it was 5 that he had a cameo.