I completed Rage, and the ending is .. meh (just my opinion). The game talked about the Authority, but I never felt like they really explained who or what they are when finishing the story up. Is there some background story on them that I missed in the game or elsewhere that gives some further explanation and story about the Authority?
The story is pretty simple so the game didn't had much to explain to begin with,wiki could have something more than you figured out but it is still very shallow.
(check the wiki link to see more links :p)
"Led by an individual known only as The Visionary, the Authority's main purpose is to restore order to the world by any means necessary, including killing unmutated humans. The Authority seems to have an agenda against Ark survivors, ruthlessly seeking them out wherever they are found and taking them back to Capital Prime for unknown reasons. However, it is speculated (through the novel and a trailer) that the reason for this is the fact that all Ark survivors have had Nanotrites implanted inside them before going into deep cryo hibernation.
It is discovered that they have their origins within the United States military. On the night that Apophis hit, the last of the Arks, a "Super Ark" capable of holding hundreds of people, was taken over by a select team of soldiers led by General Martin Cross and Colonel James Casey. With its original residents left for dead, Cross altered its programming so that it would emerge in 2105, and so be the first of the Arks to emerge in the wasteland by many years. This set up Cross and his men so that they might shape the new world in his vision."
Simply, the Authority in RAGE is a faction of Ark survivors that are seeking power. The sabotaged the timers so that they would emerge before the other cryo sleepers so they could establish themselves and then co-opt or kill anyone emerging from cold sleep.