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 the headquarters of the Green Lantern Corps.
One of the oldest planets in the universe, Oa serves as the home and headquarters for a race of blue-skinned powerful humanoids who have dubbed themselves 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—plus 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 entre of the Universe until the events of Infinite Crisis.
Oa's history is not clear; according to some stories, the Guardians originated in 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 as a desert-like, lifeless planet. The main feature is the Guardian's city. Green Lantern Corps member Hal Jordan, the Green Lantern of sector 2814 (i.e., 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 Circle of Fire event, what remains of the planet served as a base of operations for the villain Oblivion.
The planet is reformed sometime later by Jordan's old friend and associate Tom "Pie-Face" Kalmaku in the graphic novel Legacy: The Last Will and Testament of Hal Jordan. The Central Power Battery is later recharged and the Guardians resurrected shortly thereafter by Kyle Rayner after he spends some time as the near-omnipotent "Ion".
After attacks by Superboy-Prime and the Spider Guild, the Guardians fortify Oa by creating a planetwide armor and defensive system to prevent attacks against them. The full capability of the new systems are still unknown. They were not, however, enough to prevent an assault by The Sinestro Corps, which resulted in the deaths of many Green Lanterns. Afterward, the Corps doubled its defenses. However, a rogue Guardian, Scar, weakened its defenses for an attack from the Black Lantern Corps.
It is revealed in Final Crisis: Legion of 3 Worlds that Sodam Yat is the last Guardian of the Universe in the 31st century, while Rond Vidar is the last remaining Green Lantern until he is killed by Superboy-Prime's Legion of Super-Villains. Oa lies mostly in ruins, the power battery cracked, and the rings of the Corps lie in a pile, unable to locate new bearers due to the apparent death of Mogo. Statues of legacy Green Lantern Corps, including Hal Jordan, Guy Gardner, John Stewart, Kyle Rayner, Arisia, and Ch'p, line the hall where the Guardians formerly met.
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