The Guardians created the Green Lantern Corps to replace the Manhunter Robots as their force to maintain order in the universe.
At least one Green Lantern is known to have gone rogue, Sinestro of Korugar; several of his fellow Corpsmen, including John Stewart, were called into action to strip Sinestro of his power ring, prompting the former Green Lantern to swear a blood oath against the Corps.
According to Emerald Empress, Green Lanterns were a rare presence in the 30th century implying that at some point, the Green Lantern Corps disappeared.
"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."
— Oath of the Green Lanterns.
Each Green Lantern is provided with a Power ring and power battery which allows each Lantern to channel power from the central battery on the planet Oa. Rings must be recharged regularly, or they will run out of power. What the ring can do is limited only by the willpower and imagination of its user. Common uses include flight, energy beams, energy constructs, force fields, and communication. The ring also produces a green aura that can protect its user from the vacuum of space or the depths of the ocean.