In the original Star Wars: A New Hope, at the time of the filming, there were almost no characters in the film that were not played by humans in costumes. Even in the most alien-centric scene at Mos Eisley SpacePort, it was easy to see that all of the inhabitants were people in various degrees of makeup and prosthetics. This is because it was really the only option available. Later of course, there were creatures added in via computer graphics to complete scenes Lucas had not been able to previously.
But Yoda does not appear until Empire Strike Back. His character is an integral part of the story which caused the filmmakers quite a problem. The technology to bring the diminutive character to the screen had still not been invented. Audio-animatronics, like Disney had created for their theme parks, were in the early stages at this point and not quite refined enough to play on the big screen. And due to the character’s height of 66 cm (2 foot 2 in inches), a human solution wasn’t practical either.
In a recently released book, the Making of Star Wars: The Empire Strike Back, JW Rinzler revealed that the plan was initially to get a monkey to play the part. The trained animal would be dressed as Yoda with costume and mask. That sounded good, but after being warned by animal wranglers that the monkeys would not keep the mask on long enough to work, they decided to scrap the idea.
Lucas then turned to another creative genius, Jim Henson. Jim was the creator of the Muppets and a true visionary in bringing such characters to life. He had done quite a bit of extensive work on realistic puppets that could move and show emotions via complex controls. Henson was glad to help out and work began on a fully articulated hand-controlled creature. Frank Oz, also a master Muppeteer and the voice of Miss Piggy, would manipulate the puppet for the remainder of the original trilogy and much of the Phantom Menace as well as playing the voice for the last five films.
Walking scenes could not be done by a puppet and thus a diminutive actor was put into a Yoda costume and digitally shrunk further to the correct size.
In the final two films however, Yoda had a much deeper role in which wild movements were required. There was no way that a puppet could bounce off walls like he did in the battle with Dooku. Fortunately by this time CG and 3D animation had become very realistic and characters could show deep emotion and close ups with amazing detail. This allowed the producers to make the switch without causing continuity problems. In fact, the digital version had some mistakes in it, just to make the CG character act like the puppet. Yoda would later be realized once again as a CG character in the TV series Clone Wars and in various video games.
