Oa is the homeworld and headquarters of the Green Lantern Corps. The planet was severely damaged during the Parallax war.
Notable Citizens
The Green Lantern Corps: Oa is the headquarters of the Corps, but during the Parallax war, many of the Corps' members were killed and the planet was also severely damaged and as a result it has been almost deserted.
Guardians of the Universe: The Guardians were the original inhabitants of the planet and they were the ones, who made it the Corps' home but after the Parallax war the Guardians have all being killed.
The Manhunters: The Manhunters were created by the Guardians and were the Corps' predecessor but after they left Oa and the Guardians after they were re-purposed by Parallax as weapons of fear.
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 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.
The Guardians of the Universe are an alien race. They are the founders of the Green Lantern Corps.
Not much is known about the Guardians besides the fact that in their first attempt to enforce their will and guard against all menaces, about 3.5 billion years ago they created a legion of robotic sentinels called the Manhunters. However one of the Guardians was possessed by a cosmic entity known as Parallax and then re-purposed the Manhunters as weapons of fear. So as a response the Corps was created to combat the threat. In order to battle the Manhunters, the Guardians took extreme measures, as the rings powered by the emerald energy of will were not enough so they created the yellow rings, that are powered by fear. Unfortunately, the yellow light also drew something from the darkness, Parallax. During the war planet Oa was severely damaged and now all the Guardians are considered to be dead.
The Guardians evolved on the planet Maltus, and were among the first intelligent life forms in the universe. At this time they were tall greyish blue humanoids with black hair, who roughly resembled humans except for their skin color. In a pivotal moment, billions of years ago, a Maltusian named Krona used time-bending technology to observe the beginning of the Universe. However, this experiment, and later attempts to stop it, unleashed disaster upon all existence. Feeling responsible for this, the evolved Maltusians relocated to the planet Oa (at "the center of the Universe") and became the Guardians. Their goal was simple: combat evil and create an orderly universe. They acted quickly on that goal. During this period they slowly evolved into their current appearance, losing about half of their height and having their skulls grow larger. They now act as the leaders of the Green Lantern Corps, an interstellar police force which patrols the universe.
A Green Lantern is a member of an elite intergalactic police force organized to promote justice and order throughout the universe, specifically the sector they are chosen to protect. They protect and serve as part of the Green Lantern Corps formed by the Guardians of the Universe, an extraterrestrial race known as Oans. A Corps member is equipped with an item that is regarded as one of the most powerful weapons in the DC Universe, called a Green Power Ring. The Power Ring enables its bearer to manifest their thoughts into hard-light constructs and other various properties only limited by the ring's amount of power and the user's willpower and imagination. It chooses the individual and successor attributed to overcoming the great fear through the might of willpower. The Power Ring is based on advanced technology rather than having its power magically derived, as of the one of Alan Scott.
The ring is primarily used for anti-gravity, to unleash torrents of energy, translate alien dialects and to create hard-light constructs of any shape or complexity. Though, in the past, it has been unable to affect yellow-colored objects, this impurity has been overridden by Hal Jordan's power of will.
The ring must be periodically charged by contact with a Power Battery (a.k.a. Lantern), which in turn draws energy from the Guardians Of The Universe' Central Power Battery on the planet Oa, the central headquarters of the Green Lantern Corps.
Oath of the Green Lantern
In brightest day,
In blackest night,
No evil shall escape my sight,
Let those who worship evil's might,
Beware my power...Green Lantern's light!
Each member of the Green Lantern Corps is located by a green power ring for individuals that pocess strong willpower, whom can overcome great fear. The Green Power Ring is able to perform a number of abilities which can be found here: Green Power Ring.
Radiation: Besides light-based radiation used to create the energy constructs associated with a Green Lantern, the ring can simulate various forms of radiation. One example of this is the ability to simulate the radiation of Green Kryptonite, a form of radiation that is harmful to Superman. However, this ability is no longer valid and has been retconned.
Time travel: The ring allows the wielder the ability to travel through time, though the process requires great willpower.
Weaknesses
Mental Incapacitation: The ring cannot be wielded correctly if the wearer is under the influence of drugs or if there is an involvement of neural interference.
Yellow Impurity: In the beginning the Green Ring was vulnerable to the color yellow. It was unable to defend against attacks from wielders of the Sinestro Corps as well. This weakness however has now be changed and can be overcome by veterans who have the ability to face the greatest of fear. Hal Jordan was of the first of the Green Lanterns to show that this weakness could be overpowered.
Recharge: The Ring previously had to be recharged every 24 hours or when it has been depleted of energy. This can be accomplished if the bearer of the ring recites an oath into his power lantern while holding the ring directly at the light. However, the power ring now only needs to be recharged when it runs out of energy. Sinestro stated to Hal that it was possible for a Green Lantern to store his/her battery in a Pocket Universe and take it with them wherever they went, but so far Hal has not displayed the ability to do this.
Red Lantern Corps. Bearers of the Red Power Ring have the ability to drain a Green Power Ring of its energy. The ring of a Blue Lantern, however has the ability to charge a Green Lantern Ring or negate this negative effect. Blue Lanterns rings also have the ability to purge the negative effects that a Red Lanterns Ring can cause upon the wielder of a Green Lantern Ring
Ability To Kill: One of the main weaknesses of the Power Rings, that greatly disturbed Sinestro, was the fact that the bearers of the Green Lantern Ring were unable to kill. Recently however, this restriction on the rings has been lifted, but murder is still against the law of the GL Corps. This restriction was overthrown by the Guardians of the Universe during the Sinestro Corps War, in the time of desperation.
Upon recruitment, a Green Lantern is expected to uphold certain principles of his/her/its duty. These principles include:
The protection of life and liberty within the assigned sector.
Following the orders of the Guardians without question.
Noninterference with a planet's culture, political structure, or its population's collective will.
Acting within local laws and obeying the local authority within reason (presumably, the Guardians' orders can overrule this when necessary).
Taking no action against anyone or anything until they are proven to be a threat against life and liberty. Avoiding the use of equipment, resources or authority of the Corps for personal gain.
Showing respect for and cooperating with other members of the Corps and the Guardians.
Showing respect for life which includes restraint of force unless there is no reasonable alternative. Giving top priority to the greatest danger in the assigned sector.
Upholding the honor of the Corps.