Publicity Photo, Star Trek: The Motion Picture
While Shatner and Nimoy had managed to continue their careers to some extent after Star Trek went off the air (Nimoy was on Mission: Impossible for three years and had an important role in the Invasion of the Body Snatchers remake while Shatner was seen in TV movies, miniseries and was the lead actor in the short-lived Barbary Coast), the rest of the cast wasn’t so lucky.
George Takei’s credits after the series wrapped up are rather paltry: playing generic asian characters on shows like Ironside and Kung Fu and appearing in the 1970 Jerry Lewis comedy Which Way To The Front. His appearance in Star Trek: The Motion Picture, even if it generally featured him staring at the viewscreen and gawping, made him more bankable and along with the five sequel films, he made much more varied appearances on MacGyver, Miami Vice and 3rd Rock from the Sun among others. On top of that, he became a voice actor for many animated projects such as Mulan, Kim Possible and Futurama (where he played himself, of course.)
(Plus, you know, he’s the internet’s cool gay uncle now, which is pretty great.)