Ross Martin read a script when it was first given to him, then did a pen-and-ink drawing of the character he was going to play, down to the last detail, glasses, mustache, clothes, posture, shoes, et cetera. Then he brought the sketch to make-up artist Don Schoenfeld, and together they molded his face until it looked like the drawing.
Robert Conrad (5'8") wore three-inch heels as Jim West. The CBS casting office had orders not to hire any women over 5'6" for the show.
Michael Garrison, the creator of the series, died during the second season when he slipped on a spilled drink on his new marble staircase in his new home and fell down the stairs to his death.
The show was originally titled "The Wild West", but was renamed when it was decided that "The Wild Wild West" sounded better.
Robert Conrad did all of his own "fight choreography", including the stunts, until one of them backfired, nearly killing him.