Sometimes greater ages leads to greater wisdom, sometimes it leads to more intense folly. These two races which we'll now consider are their universe's oldest humanoids and, as such, accessed tremendous powers they use to achieved vastly different goals.
Earth-One's dimension was overseen a race originally called the Malthusians from the planet Malthus, journey to the center of the universe. Therein they found the planet Oa and became the Guardians of the Universe, harnessing emerald energies to empower android Manhunter agents and later the Green Lantern Corps to combat the evil spread by their evil brother, Krona at the beginning of the Multiverse.
And one such dimension in this Multiverse had a race equivalent to the Guardians in the form of the Buddak from their world of that name. Among these being were high lamas who also harnessed vast energies which they horded for themselves in order to achieve perfection. On one occasion in the 20th century, they attempted to remake Earth-Two by realigning the continents to accomplish this goal. As their own universe did not contain a counterpart of Oa (its twin was Qward in the Anti-Matter Universe), the closest equivalent was apparently Earth itself although the center of all other universes was the Rock of Eternity that originated from Earth-S. Thankfully, Doctor Fate and Earth-One's Superman stopped their evil plan, and this malevolent race disappeared thereafter. However, while residents of Malthus and Buddak reflected good and evil as parallel peoples, those of Malhtus that arrived on Oa to become the Guardians had a different class that reflected their ideals, originating on Earth-Two!
Indeed, an interesting and not widely known aspect of Alan Scott's history was one occasion as Earth-Two's Green Lantern when he was transported to the 12th century by a fake Merlin, and given his ancient power battery to recharge his ring by lamas of Tibet who guarded it. One of those who were ambassadors of China contacted him from within that same battery in the 20th century to warn him of the return of his old foe, Solomon Grundy. Another reappeared in the 1960's, seemingly still the same age, having encountered the villain known as Psycho Pirate who stole a green globe that contained remnants of the liquid metal from the original meteorite. After slaying the elderly guardian of the globe, the Pirate ultimately gained the ability to mentally manipulate Alan Scott to do his bidding, later unleashing the power of yet another remnant of the meteorite possessed by the lantern's creator, Chang. The third lama from the 12th century never reappeared.
Hal Jordan as Earth-One's Green Lantern encountered the doppleganger of the first Lama who was named Myrwhydden, a powerful enemy of Hal's predecessor Abin Sur whom Sur emprisoned within his power ring. Myrwhydden would try again and again to escape Jordan's ring unsuccessfully. Abin Sur's counterpart was the second lama/ambassador who later met Psycho Pirate. The other two were allies were other established Green Lanterns in the revered honor guard on Oa.