Agnes Moorehead was chosen to play Endora after a chance meeting with Elizabeth Montgomery and William Asher at a Bloomingdale's department store.
The show's now-iconic animated opening credits were created by Hanna-Barbera Productions, creators of such beloved 1960's cartoons as The Flintstones (1960), The Jetsons (1962), and Scooby Doo, Where Are You! (1969). These cartoon characters also guest-starred on "The Flintstones".
Elizabeth Montgomery became pregnant on three occasions during the show's run. Her first pregnancy, which occurred during the filming of episodes two through seven, wasn't used as part of the storyline, and was covered up by filming most of the scenes not featuring Montgomery first and then filming her scenes after she gave birth very soon before the season one premiere date. Her second and third pregnancies led to the births of Tabitha and Adam. Montgomery gave birth to a son in 1965, Robert Asher, while Samantha had a daughter; Montgomery's only daughter Rebecca Asher, was born in 1969 while Samantha's child was a boy.
Agnes Moorehead had a strong working relationship with Dick York, and when he was replaced by Dick Sargent, she did not take the decision well. On Sargent's first day on the set (for a script reading), and in front of the entire cast (including Sargent), Moorehead very slowly but firmly stated, "I don't like change."