Green Lantern Ring

The willpower-driven power ring that makes a Green Lantern, forged by the Guardians of the Universe.

via Wikipedia: Green Lantern Corps · see source

The Green Lantern ring, or power ring, is the tool issued to every member of the Green Lantern Corps, the intergalactic police force that the Guardians of the Universe run from the planet Oa. Driven by the wearer's willpower, it is counted among the strongest weapons in the DC Universe. A ring can shape solid energy constructs into any form its user imagines and wraps the wearer in a protective field that allows flight and survival in space. With 7204 Green Lanterns spread across 3600 sectors, the ring is the common thread that ties the whole Corps together, from Hal Jordan onward.

Quick Facts

Creators (in-universe): Guardians of the Universe
Power source: Willpower
Weakness: Limited charge; originally yellow
First ring appearance: All-American Comics #16 (1940)

Facts from the source article.

Background

The power ring predates the Corps. It first appeared in All-American Comics #16 in 1940 with Alan Scott, whose creator Martin Nodell drew on Richard Wagner's The Ring of the Nibelung and a green railway lantern. Scott's ring ran on the magical Green Flame, later explained as a piece of the Starheart. In 1959 editor Julius Schwartz reinvented Green Lantern as a science fiction hero, and in Showcase #22 a dying Green Lantern handed his ring to Hal Jordan. This new ring was a scientific device built by the Guardians, who also founded the Corps. In the late 2000s Geoff Johns and Ethan Van Sciver expanded the idea into a full emotional spectrum of rings, each color tied to its own feeling and its own Corps.

Did You Know?

Sinestro has used a yellow power ring since 1961.
A blue ring near a green one can charge it to twice its maximum power.
Red rings replace the wearer's heart and turn their blood into corrosive plasma.
The Green Lantern Corps has existed for three billion years in DC continuity.