By the time of the Battle of Naboo, Yoda was well into his 800's, making him the oldest member of the Jedi Council. He has visited hundreds of worlds on his own in his endeavor to understand and appreciate the infinitely variable nuances of the Force. The venerable Jedi Master is revered for his wisdom and insight, and prefers careful contemplation to rash action.
A long-lived Jedi Master, Yoda was the conduit for the rebirth of the nearly-vanished Jedi Knights. For more than 800 years, the diminutive green being has trained Jedi Knights in the ways of the Force, but rarely has he faced such a challenge as the impetuous young Luke Skywalker.
By the time Luke encounters him in the bogs of Dagobah, Yoda is nearly 900 years old and walks stooped over with the help of a gimer stick. He subsists on things that nature offer him, eating plants and fruits and fungi, and building his home of mud, sticks and stones.
Yoda's path to Jedi wisdom seems simple, yet profound. He makes his students unlearn what they had been taught, helping them to tune in to the subtle world around them to learn its truths. "A Jedi uses the Force for knowledge. Never for attack," he tells them.
When Emperor Palpatine ordered his purge of the Jedi, Yoda went into hiding on Dagobah. He uses the Force and the planet's own natural defenses to discourage visitors. But he has kept watch on Luke Skywalker and Leia Organa. After escaping almost certain death from a wampa ice creature on Hoth, Luke sees Ben Kenobi in a vision, telling him to go to the Dagobah system to continue his Jedi training with Yoda.
Yoda lectures young Skywalker about the Force while Luke performs rigorous physical and mental exercises. Yoda especially cautions him against the easy path of anger and the lure of the dark side of the Force.
When ordered to undertake a particularly daunting task, Luke says he'll try. "No! Try not," Yoda says. "Do. Or do not. There is no try." Despite Yoda's plea, Luke leaves before his training is complete when he senses that his friends are in danger. By the time Luke returns, Yoda is close to becoming one with the Force.