|Size matters not. Look at me. Judge me by my size, do you? Hmm? Hmm. And well you should not. For my ally is the Force, and a powerful ally it is.|Yoda, to Luke Skywalker|Star Wars Episode V: The Empire Strikes Back
Yoda was one of the most renowned and powerful Jedi Masters in Star Wars, who was known for his legendary wisdom, mastery of the Force and skills in lightsaber combat. Yoda served as a member of the Jedi High Council in the last centuries of the Galactic Republic and reigned as Grand Master of the Jedi Order before, during and after the devastating Clone Wars. Following the Battle of Geonosis Yoda held the title of Master of the Order in addition to that of Grand Master. In his centuries of service to the galaxy and the Force, Grand Master Yoda had a hand in the training of near to all the Jedi in the Order, including Obi-Wan Kenobi.
He is arguably one of the most popular characters in the Star Wars universe. His small, "cute", green, gremlin-like appearance, with such an aged face gives him an air of power and wisdom. For more canonical information in the Star Wars universe: See the page on Wookiepedia.