According to William Shatner, Leonard Nimoy “planned” Spock’s death and had good reasons for doing so. “I believe it was all planned,” he said. “I now believe (Nimoy) and Harve [Bennett] cooked this up.
“I suddenly realized that I, as well as many other people, had been taken in by the death of Spock. Leonard was so marvelous at working the territory that he got a directing job out of it.”
Shatner had no idea at the time, believing that Nimoy was finished with Trek for good. “I was thinking my good friend Nimoy is in essence saying goodbye to the whole part,” he said. “No one told me they were thinking otherwise. But I would have enjoyed being in on it. I get the secrecy. But it’s all great.”
Star Trek II: The Wrath of Khan director Nicholas Meyer disagrees with Shatner’s view of the matter. “Here’s what happened,” he said. “Leonard was very ambivalent about doing another Star Trek movie. And Harve Bennett lured him with the promise of a terrific death scene, which (Shatner) and he played so touchingly.”
Source: USA Today