 It first appeared in Green Lantern vol 2 #1, when the Guardians summoned Hal Jordan's "energy duplicate" so they could hear of his origin.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.