Green Lantern Corps
The Green Lantern Corps are the enforcers of law and order who work on behalf of Oa. Green Lanterns are individuals empowered by Oa to access the Green Central Power Battery, a repository of the cosmic energy called the Electromagnetic Emotional Spectrum.
Oans can naturally manipulate the Willpower spectrum, but the creation of the Lantern Corps allows for other life forms to use it as well. This energy is channeled using a ring shaped like the Central Power Battery and driven by focus and willpower. Lanterns are selected for their courage, focus, and personal integrity.
Of the 10,000 sectors of Oan space, no more than two Lanterns are assigned to a given area at a time. Rare exceptions are made for times of war and interstellar conflicts. Lanterns are not required to enforce the law of their homeworld, but rather to target individuals who defy interstellar peace treaties established over the millennia by Oa and other races. Lanterns serve as covert (and unwitting) informants of all activity in an area, which would be service enough for Oa. Maintaining the stability of the various regions of space serves Oan interests as well, ensuring that no empire or military force expands too quickly or snuffs out potentially recruitable primitive worlds.
The Lantern Ring
In the right hands, the Lantern Ring is arguably one of the most powerful weapons in the universe. It is partially aware, powered by an incredibly complex AI interface. Lantern Rings can be used to make constructs of 'hard light', energy fields with mass that can be formed into an infinite variety of shapes. The strength and size of these forms is limited only by the imagination of the wielder, and the Ring's software assists with generation of complex designs. Lanterns use these rings to make cages, weapons, bridges, simple machines, and anything else they can imagine. Rings are also capable of supersonic travel and hyperspace flight. They can create a personal force field which can sustain tremendous impact around the user. All rings have access to the computer databases of Oa. Lanterns can view all current information known about a topic, or historical notes going back billions of years (at least, what Oa decides they should know).