For many writers, getting a script produced by Star Trek is a feather in the cap, and one they would have especially wanted in the early days of Star Trek: The Original Series had they know how big the franchise would become. But one writer essentially begged Gene Roddenberry to kill his script.
According to Giant Freakin Robot, Conrad Spinrad's script, "He Walked Among Us," would have included Milton Berle as a Federation scientist called Bayne who'd given technology to a primitive race, the Jugali. Bayne ends up being worshipped as a god, and Captain Kirk has to get Bayne off the planet before further damage can be done.
The episode, after rewriters, would have been a comedic one, but that's not what Spinrad wanted as he'd written a serious script for Berle who was mostly known for comedy. Gene Roddenberry had wanted Berle as he was a fan, but apparently, Roddenberry wasn't aware that Berle could also play dramatic roles. To that end, when it was time for script rewrites, Roddenberry changed the serious script into what Spinrad calls "an unfunny comedy."
Spinrad was so upset and disgusted by the rewrite that he asked Roddenberry not to produce it, telling the Star Trek creator that it was lousy and should be killed. Spinrad got his wish, and the script never made it to television. That also meant Spinrad wasn't credited as a Star Trek writer. He did go on to publish the original script in ebook format for fans, though it's not currently available for purchase.