For millenia, two twin organizations have existed centered around energies originating for planet Oa. In one universe, this was a good group of guys and gals, composed of various aliens throughout the galaxy known as the Green Lantern Corps. Each individual member was assigned a sector in space to proect, and provided with a power battery and power ring allowing the wearer to perform tremendous feats. Directed by the Guardians of the Universe, the first Corps member of originate from Earth-One was Hal Jordan. On the occasions when Batman interacted with the Corps and their masters, the Guardians, it wasn't always pleasant circumstances. Such as when an intergalactic criminal when the Green Lanterns are pursuing commits crimes on Earth, causing a conflict of judisdiction between the Darknight Detective and the Emerald Crusaders. Nevertheless, they eventually reconciled when it was learned that Sinestro was behind this devious deception.
Concurrently, in the universe of Earth-Two, such emerald energies originating from the Starheart in the form of a gigantic green meteorite fell into the hands of the lampmaker Chang. Possessing his power stone derived from this radiating rock from space, Chang later assembled his Green Dragon Tong which operated for untold ages. This Tong operated rivalry to the Tibetan Lamas who cared for the meteor and Chang's Lamp. The sinister syndicate of Chang, while tracking the wielder of the power ring Alan Scott, operated in Gotham City. This Tong came into conflict with that world's Batman and Robin in the 1940's, with several of its members perishing during that period of time. Decades later, Chang reassembled his Tong into a tighter nit troop that lured Scott back to Gotham to plunder his power ring. While Chang himself had a counterpart in Shahn-Zi of Earth-One, both egomaniacal immortals, his Tong operated in a fashion similar to that of the Corps in a parallel unvierse... except without power rings. Those were possessed by Sinestro's "Sinestro Corps" of clones that briefly invade Earth-Two. During the Crisis on Infinite Earths, just as the Green Dragon Tong had been rendered non-existence without their master Chang, who had perished, so too had the Green Lantern Corps' forces been depleted when several of their members and those of the Guardians also passing away during that cosmic conflict.