Grand Master or Grandmaster, also known as Grand Jedi Master, was a title generally bestowed on the oldest and wisest Jedi. Whereas the Master of the Order served as leader of the Jedi High Council, the Grand Master was the head of the Jedi Order. The title was shared by Jedi Masters Lahru, Pra-Tre Veter, and Yoda during the High Republic Era. Yoda continued to serve as the Grand Master in the final years of the Galactic Republic, and was one of the few survivors of the Great Jedi Purge that commenced near the end of the Clone Wars.
The Grand Master oversaw the Jedi Order. The title of Grand Master was generally reserved for the oldest and wisest living Jedi Master. It was distinct from the office of Master of the Order, the holder of which led the Jedi High Council. However, it was possible for a single individual to hold both titles at the same time. The Grand Master would humbly teach the most junior members of the Order, younglings, completing the circle of Jedi training. According to Tera Sinube, it was rare for a Grand Master to train his own Padawan, and therefore regarded as an honor. Sometimes, the Jedi Order possessed multiple Grand Masters simultaneously.
During the High Republic Era, at the time of the Great Hyperspace Disaster, three Jedi shared the rank of Grand Master, including Masters Lahru, Yoda, and Pra-Tre Veter, who attended the dedication of the Starlight Beacon.
By the time of the Invasion of Naboo, two hundred years after the Great Disaster, the still-living Yoda was the sole holder of the rank of Grand Master. Yoda had trained generations of Jedi for eight centuries, and continued as Grand Master through the Clone Wars.
During the conflict in which Yoda and other members of the Order led the Grand Army of the Republic as Jedi Generals, Ki-Adi-Mundi became concerned about Yoda’s state of mind, given the Grand Master’s role in training Count Dooku prior to Dooku’s descent to the dark side of the Force. However, Obi-Wan Kenobi countered that every Jedi in their time had been apprenticed to the Grand Master, and therefore dismissed the notion that Yoda was responsible for Dooku’s actions as a Sith Lord. After the Dark Lord of the Sith Darth Sidious managed to kill the majority of Jedi throughout the galaxy, the Grand Master went into exile on the planet Dagobah.