classictrek: Immediately after the release of Star Trek III,...
Immediately after the release of Star Trek III, Paramount hired Leonard Nimoy to develop and direct the fourth installment in the series.
Perhaps feeling slighted at his compatriot’s increased involvement in the franchise, William Shatner was initially reluctant to return to Star Trek IV. This feeling was bolstered after he heard that that Nimoy and Bennett were more interested in a lighter adventure without a clear-cut villain and he out-and-out refused to appear in the next film. Without Shatner’s involvement, Nimoy and his team began early development on a prequel to the original series featuring the Starfleet Academy adventures of our crew.
After being offered the same paycheck as Nimoy ($2.5m), Shatner agreed to be in Star Trek IV, which was now a movie that would continue the “current” adventures of the magnificent seven in space.