Green Lantern is the name of several superheroes from the fictional DC Universe, all of whom are characterized by a power ring and the ability to create solid constructs with the ring.
The first Green Lantern (Alan Scott) was created by writer Bill Finger and artist Martin Nodell in All-American Comics #16 (July 1940). However, he was not related to the Green Lantern Corps other than by name, as specified in Green Lantern: Rebirth.
Each Green Lantern possesses a power ring and green lantern that gives the user great control over the physical world as long as the wielder has sufficient willpower and strength to wield it. The ring is one of the most powerful weapons in the universe and can be very dangerous. While the ring of the Golden Age Green Lantern (Alan Scott) is magically powered, the rings worn by all subsequent Lanterns are technological creations of the Guardians of the Universe, who granted such rings to worthy candidates. These individuals made up the intergalactic police force known as the Green Lantern Corps.
After World War II, when sales of superhero comic books generally declined, DC ceased publishing new adventures of Alan Scott as the Green Lantern. In 1959, at the beginning of the Silver Age of Comic Books, DC editor Julius Schwartz assigned writer John Broome and artist Gil Kane to revive the Green Lantern character, this time as test pilot Hal Jordan who became a founding member of the Justice League of America. In 1970, writer Denny O'Neil and artist Neal Adams teamed Green Lantern with archer Green Arrow in groundbreaking, socially conscious, and award-winning stories that pitted the sensibilities of the law-and-order-oriented Green Lantern with the populist Green Arrow. Several cosmically-themed series followed, as did occasional different individuals in the role of Earth's Green Lantern. Most prominent of these are Hal Jordan, John Stewart, Guy Gardner and Kyle Rayner.
Each of the Earth's Green Lanterns has been a member of either the Justice Society of America or the Justice League of America, and John Stewart was featured as one of the main characters in both the Justice League and the Justice League Unlimited animated series. The Green Lanterns are often depicted as being close friends of the various men who have been the Flash, the most notable friendships having been between Alan Scott and Jay Garrick (the Golden Age Green Lantern and Flash), Hal Jordan and Barry Allen (the Silver Age Green Lantern and Flash), Kyle Rayner and Wally West (the modern-age Green Lantern and Flash), and Jordan also being friends with West.