Zaltar was an official in Argo City, an isolated Kryptonian colony. He was charged with the care of the Omegahedron. One day he showed the miraculous power source to Kara Zor-El, which he borrowed (without permission) from the city's administration without their knowledge. However, Kara lost the Omegahedron by causing it to be sucked out into space. Zaltar personally took responsibility for its loss and was sentenced to the Phantom Zone.
Kara ventured to Earth in order to find the Omegahedron and free Zaltar. Later, when Kara as Supergirl was imprisoned in the Phantom Zone by Selena, Zaltar sacrificed his life to help her escape in order to confront Selena and defeat her, thus being able to return the Omegahedron to Argo City.