Leonard Nimoy Made Star Trek's 1970s Animated Series Better

Star Trek: The Animated Series would have omitted a significant portion of the cast from Star Trek: The Original Series had Leonard Nimoy not intervened. TOS was canceled in 1969 after three seasons, but the show became a pop culture sensation over the next few years in syndication. While it wasn't yet feasible to bring the show back in live action, NBC decided to produce an animated revival in 1973.

Source: Screenrant