In 1969, fan pressure forces NBC to renew Star Trek for a fourth season, in spite of its low ratings. They move it from the Friday night "death slot" they had placed it in to a more congenial Thursday at 7PM, and, to their great surprise, the series shots up in the ratings.
Fourth Season of Star Trek by Robbie TaylorThe fourth season is greeted by fans as the show's best yet, and it climbs from the cellar of the Nielson's to the #4 spot. Advertising picks up on the show, and NBC gives it a 5th season.
The show hits its stride as critics come aboard, hailing the writing and acting on the series, and Star Trek spends most of season five as the number 1 show on television. Although its creator, Gene Roddenberry, had planned to end the series after 5 years, and even had the show's intro state that the Enterprise was on a "5-year mission," he was easily convinced to extend that to six, seven and then eight. William Shatner's opening lines were changed from a 5-year mission to "continuing mission".
NBC was more than willing to renew the series for ninth season, but stars William Shatner, Leonard Nimoy, James Doohan and others were ready to move on to other projects. They did reunite for several feature films later on, and George Takei's character Sulu was given his own spinoff series, "Excelsior", in 1976.