Stuart Freeborn designed the appearance of Yoda, by using his own facial likeness as inspiration and adding wrinkles that he compared to that of Albert Einstein. The set of Dagobah was actually built five feet above the ground, which allowed the likes of Frank Oz to successfully puppet Yoda. Despite the communication difficulties this caused, the end result was a revolutionary use of practical effects.
It is known that, originally, it would have been Obi-Wan training Luke, but then George Lucas decided that it wouldn’t make sense to have him standing next to Luke in all the films and not help him fight, and that’s why he is killed in the first film. He then created Yoda to have someone that would train Luke.
Later, in The Phantom Menace, Yoda was redesigned to look younger, and was computer-generated for some distant shots but he remained mostly a puppet, based on the one made by Stuart Freeborn for the first trilogy.
