Oa is a fictional planet that lies at the center of the DC Comics universe. Since its inception, Oa has been the planetary citadel of the Guardians of the Universe and headquarters of the Green Lantern Corps. It first appeared in Green Lantern (vol. 2) #1, when the Guardians summoned Hal Jordan's "energy duplicate" so they could hear of his origin. History One of the oldest planets in the universe, Oa serves as the home and headquarters for a race of blue-skinned powerful humanoids called the Guardians of the Universe. The Guardians administer the Green Lantern Corps, a group of powerful universal police officers equipped by the Guardians with green-colored power rings along with green lanterns with which to charge the rings. According to the story "Heart of a Star" in the Sandman: Endless Nights graphic novel, Oa's star is called Sto-Oa (the Light of Oa) by the children of the planet's inhabitants. Its location has been firmly established by numerous references in Green Lantern comics over the years. It was formerly the center of the universe until the events of Infinite Crisis. Oa's history is not clear; according to some stories, the Guardians originated on a planet called Maltus. These evolved Maltusians later moved to Oa and named themselves Oans. Oa became a convenient base of operations. Other stories had the Oans living there from the beginning. Oa appears primarily as a desert-like, lifeless planet except for the Guardians' city which contains the Corps Central Battery and various halls, living quarters, containment cells and training centers for the Green Lantern Corps. It serves basically as a planet-sized all-in-one police station, training grounds and prison. During a period where the planet had been abandoned and the Central Battery destroyed, Oa spent some time as a patchwork mosaic of cities from other planets similar to Battleworld. This transformation was due to a rogue Guardian driven insane by solitude. When the Guardians returned to Oa, Mosaic was kept as an experiment in inter-galactic cooperative living. Green Lantern Corps member Hal Jordan, the Green Lantern of sector 2814 (which includes Earth), under the influence of the evil entity Parallax, kills all but one of the Guardians and most of the Corps before draining Oa's Central Power Battery of its energy. During the final Zero Hour: Crisis in Time battle with Hal Jordan, Kyle Rayner destroys the planet in an attempt to defeat Hal.