A member of the Jedi Order took on Yoda as a Padawan when Yoda was young, more than eight hundred years before the reign of the Galactic Empire. At some point, the Jedi told Yoda an insightful story about a Jedi named K’ungfu, and taught him how to live in peace.
Sometime before the Invasion of Naboo in 32 BBY, Jedi Master Yoda swore to pass on his Master’s teachings and end the war between local human tribes and giants of living stone on a planet in the Vagadarr system. When Yoda had become the last Jedi Master in existence, he told his Master’s story about K’ungfu to Luke Skywalker during the latter’s Jedi training on the planet Dagobah in 3 ABY.
Yoda’s old Master was first mentioned, albeit unnamed, in the new Star Wars canon in The Empire Strikes Back: So You Want to Be a Jedi?, a young-readers book which retells the events of the 1980 film Star Wars: Episode V The Empire Strikes Back. The book was written by Adam Gidwitz and published in 2015.
Within the Star Wars Legends continuity, Yoda’s instructor was established as N’Kata Del Gormo, a male Hysalrian Jedi Master, according to an in-universe legend. The character was created by Chuck Hamilton, a Star Wars fan, for the backstory of his Hysalrian entry in the «Design An Alien» contest held in the Star Wars Galaxy Magazine. Hamilton’s entry was given an honorable mention in the ninth issue of the magazine, released on October 1, 1996.