Jedi Master Vodo-Siosk Baas lived 4,000 years before the Battle of Yavin and trained Jedi on the planet of Dantooine. In addition to training Jedi, he was also a noted Jedi Historian and a gatekeeper of one of the Jedi Holocrons. He also spent time at the Jedi Library on Ossus instructing students in lightsaber construction. He helped Nomi Sunrider build her first lightsaber.
Three of his most notable students were Exar Kun , and two Cathar Jedi, Sylvar and Crado . One day while dueling, Kun easily defeated Crado and was put up against Sylvar. Sylvar and Crado were mates and she was enraged at how Kun had so easily defeated and embarrassed Crado. Master Vodo was testing Sylvar's anger and she failed the test and in the midst of her duel with Kun, lashed out with her claws and cut Kun across his face. This wound would leave a permanent scar on his face. An enraged Exar Kun lashed out at Sylvar with all his might and Master Baas had to step in and intervene. Vodo disarmed Kun with his staff but then was challenged directly by Kun, who had retrieved Crado's lightsaber through the force. Kun dueled with his master and was finally able to defeat him with the assistance of a second lighsaber. Master Vodo told Kun that he was his strongest and most gifted student, but he sensed something missing inside of him, an emptiness. Kun made the decision to leave Dantooine, claiming that he learned all he could from his master and declared himself a full Jed Knight
Master Vodo had a good idea where that emptiness would lead Exar Kun. He had previously caught Kun learning about the Sith and the Dark Side from the Jedi Holocron. Kun was caught listening to the story of Naga Sadow and Freedon Nadd. Master Vodo told Kun he was not ready to learn of the dark side. He knew that Kun's arrogance might lead him to look too far into such lore and lead him down the path to the Dark Side.
A Dark Side cult called the Krath had taken over the Empress Teta System and a Jedi conclave was called. While travelling to the Conclave, Master Vodo felt a great disturbance in the force and sensed that it was his former apprentice Exar Kun succumbing to the Dark Side and becoming a Dark Lord of the Sith. Vodo tried to assist his former student through the Force but the Dark Forces surrounding Kun were too strong.
When the Great Sith War broke out and the new Dark Lord of the Sith Exar Kun and his apprentice Ulic Qel-Droma waged war against the Jedi and the Republic, Master Vodo was one of the prominent Jedi Leaders. Unfortunately, one of Master Vodo's other students would become seduced by Kun and his teachings. Crado would abandon the Jedi and become of Kun's Lieutenants. When Ulic Qel-Droma was on trial after he was captured during his attack on Coruscant, Master Vodo was one of the Jedi Masters present. Qel-Droma was sentenced to death, but Exar Kun burst into the room before the sentence could be carried out. Master Vodo intervened and engaged Kun in a duel before the Sith Lord could do too much damage. They were fairly evenly matched, but then Kun unveiled his new dual bladed lightsaber. The double bladed weapon allowed him to easily defeat and killed his former master. Master Vodo's body disappeared as he became one with the Force.
The teachings of Master Vodo-Siosk Baas became part of his Jedi Holocron. The holocron eventually came into the posession of Emperor Palpatine. It is unknown whether he gained it prior to the Jedi Purge or after, but he would use the teachings it contained to help him transfer his spirit to a clone body after he was killed on the second Death Star.
After the Palpatine clone was defeated by Princess Leia and her brother Luke Skywalker, the holocron became property of the Jedi once again. In the decade after the fall of the Empire, Exar Kun's spirit began to have a dark influence on the Jedi students at Luke Skywalker's new Jedi Academy. With the assistance of the Jedi Holocron and the teachings of Master Vodo wich were contained within it, the Jedi banded together to bind and destroy Exar Kun forever.