Green Lantern

Green Lantern is the name of several fictional characters, superheroes appearing in comic books published by DC Comics. Each Green Lantern possesses a power ring that gives the user great control over the physical world as long as the wielder has sufficient willpower and strength to wield it. While the ring of the Golden Age Green Lantern was magically powered, the rings worn by all subsequent Lanterns were 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.

Leonard: (trying to work out how to get a heavy box up the stairs) Do you have any ideas?

Sheldon: Yes, but they all involve a Green Lantern and a power ring. (0102)

The boys discuss the vulnerabilities of Green Lantern. Raj is annoyed by the fact that Green Lantern can be defeated by the colour yellow (0219).

Raj had a collectable Green Lantern lantern (available here), but gave it to Sheldon to bribe him into accompanying Raj to a university mixer as his wingman (0312). NOTE: The correct name for this device is the Green Lantern Power Battery. Sheldon should have known this ...

Sheldon is often depicted wearing shirts of the various different Corps that appear in the Green Lantern series (i. e. Red Lanterns, Orange Lanterns, etc.). In the comics, each color represents a specific emotion: Red=Anger, Orange=Greed, Yellow=Fear, Green=Willpower, Blue=Hope, Indigo=Compassion, Violet=Love. Not surprisingly, whichever shirt Sheldon happens to be wearing is often a clue to his mood in a given scene.