Green Lantern began in the Golden Age as Alan Scott, a costumed adventurer with a ring that let his imagination take shape but could not affect wood. He was a member of the Justice Society of America.
Shen DC revived their old super-heroes characters in new incarnations in the late 1950s and early 1960s, Green Lantern was reborn as Hal Jordan, a test pilot who received a ring similar to his predecessor — but now with a weakness for the color yellow, as opposed to wood. Jordan discovered that he was only one member of Green Lantern Corps, a cosmic police force run by the impish, blue-skinned Guardians.
Other members of the Green Lantern Corps were introduced over the years, including other human members. In the 1990s, Hal Jordan became a villain and destroyed the Corps, leaving new character Kryle Rayner (almost) the last Green Lantern. Other Green Lanterns were introduced and re-introduced, and Hal Jordan ultimately returned. Now, the Green Lantern Corps was revealed as only one of a spectrum of different multi-colored Lantern Corps, each tied to a specific emotion.