As a lieutenant commander, Ann Mulhall has the distinction of being the highest-ranking female Starfleet character shown in The Original Series.
The voice of Sargon was played by James Doohan. Sargon of Akkad was a Mesopotamian king, who by most accounts, began ruling around 2269 B.C. In the show the year is around 2268 A.D.
This episode marks George Takei's return to the series after an absence of some months while filming The Green Berets (1968). His last appearance was I, Mudd (1967), which was ten episodes earlier in production order.
First Star Trek appearance of Diana Muldaur. She would also appear as Miranda Jones in the episode Is There in Truth No Beauty? (1968), and as Dr. Kathryn Pulaski in 20 episodes of Star Trek: The Next Generation (1987).
Writer John T. Dugan wrote the original script of this episode after he had read an article about highly sophisticated robots. In his original draft, Sargon and Thalassa continue their existence as spirits without bodies, floating around the universe. However, Gene Roddenberry, who did an uncredited re-write on the script, changed the ending to the aliens fading out into oblivion. This led to Dugan using his pen-name John Kingsbridge in the episode's credits.