Green Lantern Corps (Earth-6531)

"Since time memorial, the Green Lantern Corps has served as the keepers of peace, order, and justice through the galaxy. To be chosen to join its ranks is the highest of honors, and the greatest of responsibilities."

- - Tomar-Re to Hal Jordan

The Green Lantern Corps is a interstellar law enforcement organization based on the planet Oa. Having existed for three million years, the Green Lantern Corps hold stewardship over the universe by orders of the Guardians of the Universe, harnessing the strength of Willpower with their power rings. Through their history, its members have suffered multiple conflicts, both from outside and inside, and they currently have 3600 sectors through the universe under their jurisdiction. The Corps currently have 7202 members, who are individually known as Green Lanterns.

Early History
Millions of years in the past, the Oans settled on Oa after escaping from their planet's destruction at the hands of the Celestials. On Oa, they found about the Emotional Electromagnetic Spectrum, an energy which could manifest in eight forms: Willpower, Fear, Rage, Compassion, Avarice, Love, Life, and Death. The planet in particular was rich with Willpower, manifested through a green light, and so the Oans decided to harness it with their advanced technology.

Parallax and the Manhunters
However, the Oans also found about Fear, manifested through a yellow light. They did not dare to risk succumbing to Fear, as they knew it could shape even their most beloved ones into something they couldn't recognize. One of them, Krona, however, sought to manipulate the energy, as he though it could serve as a better weapon for them to use against any threat. When he attempted to use it, the yellow energy absorbed him and transformed Krona into a being made of Fear itself known as Parallax.

The Oans assembled themselves and managed to defeat Parallax, banishing him to a frozen planet at the edges of the Milky Way galaxy. Seeing the power they had, the Oans named themselves Guardians of the Universe, and started using the energy of Willpower to power the Manhunters, a race of robotic beings that would serve as the Guardians' own police peace-keeping force through the galaxy.

Oath
"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!"