lunatechian (lunatech-ian)

When George Lucas and screenwriter Lawrence Kasdan decided to make the ancient Jedi at the heart of Luke's spiritual journey into a two-foot tall, pointy-eared alien, it wasn't clear how the character could actually be realized on screen using 1980 technology. At the time, animatronic technology wasn't thought to be advanced enough to pull off Yoda. .... they decided to try putting a trained monkey in a Yoda costume, including a full Yoda face mask. Rinzler showed a picture of the monkey on set, but he explained this idea was quickly abandoned when one of the people who worked on the primate scenes in 2001: A Space Odyssey pointed out "Look, the monkey's just going to pull off the mask over and over again. It's never going to work."

In the picture, a monkey is outfitted with a cane and a mask and measured. The simian was also briefly considered for walking shots of Minch-Yoda that would have been impossible to execute with a puppet.

Pic taken from Vanity Fair