For more than eight hundred years, the diminutive creature known as Yoda trained only the most serious and commited students in the ways of the force. In the beginning (before he joined the Jedi council), Yoda spent most of his life time aboard the Ch'unthor, a spaceship dedicated to the training of Jedi Apprentices. Yoda's origins are steeped in mystery. His species is unknown, but he was green skinned, with large, brown bulbous eyes, white hair, and long ears. Although he walked on two feet, they were reptilian tridactyl feet. His hands like-wise were claws. And by the time Luke Skywalker met the Jedi Master, Yoda was nine hundred years old, walking with the aid of a gimer stick.
Yoda built his home of mud, sticks, stones, and other natural materials from Dagobah. The windows were made from transparent gems. Yoda lived near a lagoon so he listen to the lulling sound of rain falling on water. He ate plants, fruits, and fungi, subsisting on the things nature offered.
Before the Jedi Knights were ordered to be purged from the galaxy by the Emperor, Yoda was one of the 12 members of the august and powerful Jedi Council on Coruscant. He was with fellow members (such as Ki-Adi-Mundi and Plo Koon) when they watched as a young Anakin Skywalker faced probing questions from another senoir Jedi, Mace Windu, the beginning of a dangerous future for the boy destined to be a Dark Lord of the Sith.
Though Yoda never trained Anakin himself, one of his students, the young and reckless Obi-Wan Kenobi, did. Kenobi, his final student before the coming of Luke Skywalker (decades later), was one of the last Jedi to survive under Palpatine's rule in seclusion on the desert planet of Tatooine.
Yoda taught his students that affinity with nature enhanced an affinity with the Force. He gave them endurance tests, had them run marathons, jump wide lagoons, fight seeker balls with their lightsabers, balance in seemingly impossible ways, meditating for long periods, and levitate objects. Yoda made his students unlearn that which their upbringings, and their own eyes and ears, had taught them.
"A Jedi uses the Force for knowledge. Never for attack." Lessons such as these made training easier; they also became good advice to pass on to future Jedi.
When Palpatine ordered the Jedi Knights purged from the Galaxy, Yoda went deeper into hiding on Dagobah. Using the Force and the planet's natural defenses, Yoda was able to dicourage visitors, even as his students and his students' students were slaughtered by Darth Vader and Palpatine's men. Since Vader had been trained solely by Kenobi, he seemed not to know of Yoda's existence, and Palpatine either forgot about Yoda or thought he had already died. Either way, Yoda escaped the purge.
Yoda kept a Force watch on Luke Skywalker and Leia Organa as their destinies took shape. Obi-Wan wanted to tell Luke about his father earlier in Skywalker's teen years, but Yoda told him to wait. But after Kenobi's temporal death, Yoda knew the training of his last Jedi student must commence soon.
On hoth, an injured Luke Skywalker was visited by the life force of Obi-Wan Kenobi. Ben told him to go to the Dagobah system to learn from Yoda, "the Jedi Master who instructed me." So when the rebels evacuated the ice planet, Luke flew his X-Wing to the boggy planet. It crashed into the swamps, leaving Luke and R2-D2 only a few supplies to survive off of.
Yoda approached the duo, offering help, but not revealing who he was. When luke admitted he was looking for a great warrior, Yoda chuckled, telling him "wars not make one great," then offered to take them to go see Yoda.
Back at the cramped hut, Yoda tried to be hospitable, giving Luke some rootleaf stew, but Luke was impatient. Frustrated, Yoda complained that Luke was unteachable and full of anger and recklessness. "Was I any different when you taught me?" the nearby spirit of Ben Kenobi asked. Then Luke realized he was in the presence of Yoda, and promised that he would do whatever it took to become a Jedi.
Yoda commenced training Luke immediatly, lecturing him about the Force while Luke performed rigorous physical and phychological exercises. He especially warned Luke against the path of anger, the lure of the dark side. He tested Luke by allowing him to go into a tree that was filled with dark-side energy. There Luke dueled with an apparition that resembeled Darth Vader, until the helmit cracked and Luke saw his own face. The young Jedi has learned a valuable lesson about the dark side possibilities that lay in his future.
Luke learned two other valuable lessons. Once, when Yoda had him pratice levitation, Skywalker was distracted when his X-wing sank in the bog, and he gave into despair. Yoda ordered him to use the same levitation powers to raise his ship. Luke said he'd trty, but was cut off curtly by Yoda "No! Try not. Do. Or do not. There is no try!"
Lacking belief in himself or his powers, Luke was unable to raise his ship, complaining that it was to big. "Size matters not," Yoda told him, reminding him that the force flows through everything...throught Luke, through the bog, and through his ship. Then Yoda concentrated and grandly raised the X-wing out of the marsh and onto dry land. "I don't believe it," his astonished student said.
"That is why you fail, Yoda told him.
Days later, Yoda instructed Luke to open his mind to memories of old friends, and to the possibilities of the future. Jarred by the visions of Han Solo and Leia in pain on Cloud City, Luke demanded to rescue them. Yoda and the spirit of Kenobi both warned Luke that the decision could destroy everything thay had fought for, and that he was still much too susceptible to the dark side.
Torn between this knowledge and the visions of his friends in danger, Luke decided to leave dagobah. He promised to return to complete his training, and took off in his X-wing. After Luke left, Yoda and Ben discussed the future of the Jedi, with Yodareminding Ben that there was "another" hope. He was referring to Leia.
Luke was not lost to the dark side, and the followinf year he returned to Dagobah, as he had sworn to do. But he found that Yoda was dying. Yet the diminutive Jedi Master joked that Luke would not look nearly so good at nine hundred years old.
Then Yoda offered his final advice. He once again warned Luke to beware the darke side, even though a confrontation with Darth Vader was a necessity. Reminding Luke that he ws now the last of the Jedi, Yoda's final words were to reveal that there was another Skywalker. Then Yoda breathed his last breath and disappeared, becoming one with the Force.
When Luke and the Alliance were victorious in the Battle of Endor, a celebration was held. There, for a few moments, Luke saw Obi-wann Kenobi, Yoda, and Anakin Skywalker, all smiling to him. Kenobi and Yoda's pupil-Skywalker's som-was, now and forever, a Jedi.