Edward G. Robinson was originally chosen to play Dr. Zaius, but had to drop out due to health concerns. He was replaced by Maurice Evans, better known to classic TV fans as Samantha's father from "Bewitched" (see photo).
"Twilight Zone" creator Rod Serling co-wrote the screenplay for the first film in the series.
While Ricardo Montalban and Roddy McDowall (as both Cornelius and Caesar) played friends in the Apes series of films, Roddy would later go on to guest star as Mr. Roarke's nemesis, Satan, on "Fantasy Island.