Ulaz is 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 doctor, he helped Shiro escape. He uploaded the coordinates of the Blade of Marmora base into Shiro's robotic arm and send 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 has 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.