Ulaz was a member of the Blade of Marmora, a Galra resistance group. He worked as a spy in one of the ships ruled by Zarkon. Disguised as a doctor, he helped Shiro escape. He then uploaded the coordinates of the Blade of Marmora base into Shiro's robotic arm and sent him out in an escape pod.
While in a recovery tank Shiro remembers Ulaz helping him. Using the coordinates he got from him, Shiro and the team head out to that location. There the ship is intruded by a mysterious person who reveals himself to be Ulaz after recognizing Shiro mid-fight.
Allura is skeptical about Ulaz's loyalty because 'no Galra can be trusted'. But he is revealed to have no ill intentions; in fact he wants to help them.
Zarkon manages to track the paladins and sends the now Robotic Beast (RoBeast) Prorok to them. Voltron has a hard time keeping the RoBeast at bay. They are saved by Ulaz, who sacrifices himself and his ship by crashing into the monster.