The aliens were survivors of a doomed planet that made their presence known to Ralph Hinkley and Bill Maxwell, the main protagonists of the series. They gave Ralph his super suit and instructed them to fight the forces of evil together. They keep multiple beings (mostly humans) in suspended animation aboard their ship. The reason for this is unknown but Bill guessed that they were their replacements, as in the event of Ralph and Bill going rougue, they would still need someone to use the suit. (Vanity, Says the Preacher)
The aliens can greatly effect the world even without being present. This is displayed by manipulation of objects and machines. They also have an unknown way of healing people who have been gravely wounded like Ralph and others. When Ralph’s identity was revealed they were able to erase this knowledge from the world if he gave up the suit. (The Greatest American Heroine) They also have the ability to revive the dead, who then speak with a curious echoing speech pattern, and apparently live forever. Interestingly, the revival of the dead does not appear to heal their wounds, as both United States Sgt. Jenson and Bill's partner, FBI agent John Mackie, kept their wounds (Bullet wounds, in John's case, and bruises from the electrocution that killed Jenson) after they were revived. Strangely, while John seems to have been simply revived, and kept his personality and regular human attributes, Sgt. Jenson seemed to be only a vehicle for the Alien's communication, and appeared to be able to teleport.
The aliens are somewhat short, with green skin, holes for ears, and four fingers on each hand. They wear silver bodysuits that bear the same symbol as Ralph's super suit (The "scissors" symbol").
They appear to have another species of alien as their servants/helpers. These aliens are shorter, and appear to float on a whispy ghost/genielike tail, as they lack legs. They also have four fingers on each hand, and have darker green skin. They sport a long brown antennae on their heads, with a white point at the tip. They appear to wear a white suit (without the symbol) for purely uniform purposes.
Interestingly, in both the pilot episode, and on episode 11, "Operation Spoilsport," the aliens communicate by hijacking the radio waves and tuning in to different stations to find the words they want to use, but on the final episode, "Vanity Says the Preacher," they have technology that allows them to speak directly to Ralph and Bill.