The voice of the keeper was done by actor Malachi Throne.
When footage of The Cage was used for the two part episode The Menagerie additional dialog for the Keeper needed to be recorded because the character addresses Captain Kirk by name. Throne was called in to reprise his voiceover and was also cast as Commodore Mendez (most likely a cost saving measure–two birds with one stone, so to speak). During post production it became obvious with repeated listening's of the audio track that the Keeper and the Mendez character's voice were done by the same actor. To solve this problem the recording of Throne's Keeper voice had its pitch changed.
Long before digital pitch shifters, there was the Eltro Information Rate Changer, a 1/4" tape machine with four play heads mounted on a rotating drum.
There is a photo of the Mark II Eltro Information Rate Changer hardware unit at the link below [thanks Capt.Mac
and here is another very famous example of this analog audio processing tool used on a voice:
Yep. And "Rate Changer" = "Tempophon" See the discussion previously in this thread as well as the photo in this link: http://icasea.blogspot.com/2009/10/s...empophone.html
Also, this link has a cool video showing how the "phonogene" -- the granddaddy term -- essentially operates: http://www.joostnieuwenburg.nl/heads.html