Star Trek: The Animated Series were added to the cast—claiming that Sulu and Uhura were of importance as they were proof of the ethnic diversity of the 23rd century and should not be recast. Nimoy also took this stand as a matter of principle, as he knew of the financial troubles many of his "Star Trek" co-stars were facing after cancellation of the series. Koenig was not forgotten, and later wrote an episode for the series, becoming the first "Star Trek" actor to write a "Star Trek" story. Koenig wrote "The Infinite Vulcan", which had plot elements from the original "Star Trek" episode "Space Seed"
Star Trek: The Original Series had a "quality audience" including "upper-income, better-educated males", and other NBC shows had lower overall ratings. The show was unusual at the time in its serious discussion of contemporary societal issues in a futuristic context, unlike "Lost in Space" which was more "campy" in nature. The enthusiasm of "Star Trek"s viewers surprised NBC. The network had already received 29,000 fan letters for the show during its first season, more than for any other except "The Monkees". When rumors spread in late 1967 that "Star Trek" was at risk of cancellation, Roddenberry secretly began and funded an effort by Bjo Trimble,