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. When the scientist Krona tried to discover th
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. When the scientist Krona tried to discover the creation of the Universe a wave of evil engulfed the worlds and created an Anti-matter Universe of evil. He was exiled for this crime and the Oans tried to protect the Universe.
Oa Then and Now
One of the oldest planets, Oa serves as the home and headquarters of the Guardians of the Universe, who administer the Green Lantern Corps. Oa's star is called Sto-Oa (the "Light of Oa") by the children of the planet's inhabitants.
Oa appears to be mainly a desert-like, lifeless planet. The main feature is the Guardian's city which includes, among other things, the Main Power Battery that is charged by the Guardians with their own unique green energy. The Battery then broadcasts this energy to the personal Power Batteries of all Green Lanterns. This Battery has been destroyed and restored in various occasions. The first major incident was when, following the apparent execution of the renegade Sinestro, the Battery blew up, stripping almost every Green Lantern of their power rings. Oa became desolated following the catastrophe, with the former Guardian Appa Ali Apsa as its only resident, who looked over the remaining energies of the Battery.
Main article: Green Lantern: The Road Back
The solitude drove the Guardian insane, and he tapped the powers from Oa's core (along with the ring of the kidnapped John Stewart) to kidnap entire cities from different planets and create a patchwork community to keep him company. Appa held a tight telepathic control over all residents, but he was ultimately defeated by the combined efforts of Hal Jordan's bold strategies and the powers of the original Guardians of the Universe, who returned from their interdimensional retreat.
The return of the Guardians to Oa marked the beginning of the reconstruction of the Green Lantern Corps. The masters kept the Mosaic World as an experiment to see if it was possible to build an utopia from that patchwork community. For that matter, they appointed John Stewart to look over its residents until the proper time came to allow them to return to their respective homeworlds.
The Green Lantern Hal Jordan, under the influence of the evil entity Parallax, killed all but one of the Guardians and most of the Corps before draining the battery of its energy. The planet was later destroyed during a battle between Jordan and his successor, Green Lantern Kyle Rayner.
The planet was reformed sometime later by Jordan's old friend and associate Tom Kalmaku. The Central Power Battery was later recharged and the Guardians resurrected shortly thereafter by Kyle Rayner after he spent some time as the near-omnipotent "Ion".
After attacks by Superman-Prime and the Spider Guild, the Guardians refortified Oa by creating a planetwide armor and defensive system to prevent successful attacks against them. The full capability of the new systems are still unknown. They were not however able to prevent an assault by The Sinestro Corps. Afterward, the Corps doubled its defenses. However, a rogue Guardian, Scar, weakened its defenses for an attack from the Black Lantern Corps.
By the 31st century, Oa lies mostly in ruins and its 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. Green Lantern Sodam Yat became the last Guardian of the Universe in this period and subsequently recharges the power rings on Oa to rebuild the Green Lantern Corps.
One hundred years later, in the 32nd century, having discovered the true purpose of the Emotional Spectrum, the Templar Guardians evolved into energy beings known as the Elders of Oa, returned to their former home and reshaped it into a fortress of golden light. Here the Green Lanterns evolved into the Gold Lanterns. When the Gold Lantern and Legion of Super-Heroes member Kala Lour captured the traitorous Rimborian leader Crav, the General Nah, he brought him to Oa, alongisde his fellow Legion members Blok and Brainiac-5. There the Elders imprisoned the outraged Rimborian with the Light of Eternal Justice. 
Points of Interest
- Central Meeting Hall: Where Green Lanterns receive their briefing and assignments.
- Central Power Battery of Oa
- The Foundry: Forge of the Green Lantern rings and the Green Lantern battery. It is underground about two miles from the Central Power Battery and is guarded by an alien creature.
- Dining Hall: can accommodate any Green Lantern's nutritional needs. The Executive Chef, Greet, specializes in replicating dishes from across the universe. However, he has trouble replicating the vast number of foods from Earth.
- Hall of Great Service: Housing the massive Book of Oa — the Corps' lawbook and holy text — the Hall of Great Service is a library of the stories and deeds of the finest Green Lanterns of all time. like his father before him, Tomar-Tu recently took the position of Archivist Superior, filing every tale as it comes in. The Book of Oa has been designated off-limits after being rewritten by the Guardians of the Universe to include ten new laws. The library also carries records of Green Lanterns Corps and momentos of their victories and defeats.
- Hazard Simulation Facility: Where new Green Lanterns endure a series of tests to determine their viability in the field. The hazard simulation facility allows for safe, non-lethal training scenarios to be enacted.
- Memorial Hall: Erected to dedicate Green Lanterns members who lost their lives in the line of duty. Morro, a Green Lantern from the planet Sarc, and his four pets, called Dratures, volunteer as cryptkeepers.
- New Warriors: New Warriors is a themed-eatery and drinking establishment built by Guy Gardner. He decided to create the lounge after permanently relocating to Oa, modelled after his old bar on Earth.
- Planetary Citadel: The planetary citadel is the Guardians' stronghold and meeting room. It contains a holographic map of the universe, allowing them to locate disturbances and track their Green Lanterns.
- Sector Houses: These safe houses allow Lanterns to hold criminals as they await escort back to the Oan Sciencells. Limited recreational facilities are available to accommodate Green Lanterns in their travels.
- The Sciencells: a prison designed to contain the most ruthless and powerful criminals in the universe captured by the Green Lantern Corps. Its current residents include Lyssa Drak, Evil Star, Igneous Man, and Alexander Nero. Despero is possibly also currently one of its residents after a battle with the Justice League at Wayne Manor during Infinite Crisis.
- "Heart of A Star" in the Sandman: Endless Nights graphic novel
- Green Lantern Corps #222 - #224
- Green Lantern: Mosaic #10
- Green Lantern: Mosaic #18
- Green Lantern (Volume 3) #50
- Green Lantern Legacy: The Last Will and Testament of Hal Jordan
- Final Crisis: Legion of 3 Worlds #3
- Final Crisis: Legion of 3 Worlds #5
- Legion of Super-Heroes (Volume 8) #10
- Tales of the Green Lantern Corps #2