Originally, the Nova Corps was Xandar's space militia and exploration division. It consisted of 500 soldiers ranging in rank from Corpsman up to Centurion and its leader, Centurion Nova Prime. The Corps also had a regiment of Syfon Warriors, of which Powerhouse was one. After the reformation of Xandar, the Nova Corps expanded its protective range to include the entire Andromeda Galaxy and Earth. They are also known as the Xandarian StarCorps. Queen Adora (in the role of Prime Commandant) has ultimate authority of the Nova Corps.
The source the Corps' power is called the Nova Force. This is a nearly limitless energy field generated by the a living supercomputer called the Xandarian Worldmind. The energy is then transmitted into the centurions at varying levels depending on their rank. The Worldmind contains the entire record of Xandarian history and civilization.
The Green Lantern Corps are an inter-galactic police force dedicated to protecting sentient life in every form, established thousands of years ago by the Guardians. Officers are chosen for their ability to overcome great fear and given a power ring fueled by the strength of their willpower, the mightiest weapon in the universe. They have two representatives for all of the 3600 sectors in the known universe, their headquarters located centrally on the planet Oa.
The second book, First Lensman, concerns the early formation of the Galactic Patrol and the first Lens, given to First Lensman Virgil Samms of "Tellus" (Earth). Samms is one side of the vast Arisian breeding program which will produce Clarissa MacDougal, the female half of the penultimate result of their breeding program. Moreover, along with Roderick Kinnison (a member of the other side, which will produce the male half), they are natural leaders as they are supremely intelligent, forceful, and capable. The Arisians, through the scientist Bergenholm (actually an Arisian entity appearing as a human, and who "invented" the interstellar drive), make it known that if Samms, the head of the Triplanetary Service which administers law enforcement to Tellus, Mars and Venus, visits the Arisian planetary system—and only if he visits the Arisian system—he will be given the tool he needs to build the Patrol he dreams of. That tool is the Lens. The Arisians further promise him that no entity unworthy of the Lens will ever be permitted to wear it, but that he and his successors will have to discover for themselves most of its abilities. They otherwise maintain a highly distant profile and refuse to talk to other beings, stating that they have given civilization the tool it needs to bring about a good future and that people should otherwise not have reason to contact them.
In the Lensman novels, the Galactic Patrol was a combination military force and interstellar law-enforcement agency, charged with the defense and preservation of Civilization. The Lensmen were the elite of the Galactic Patrol, and Lensmen tended to hold the majority of the senior-executive positions in the Patrol, although non-Lensmen personnel were essential to the organization's success, and garnered almost as much respect as their Lens-bearing superiors. The organization had large numbers of non-humans serving in all roles, although many of the leadership positions seem to be occupied by humanity.