The Guardians evolved on the planet Maltus, and were possibly the first intelligent life forms in the Universe. At this time, they were tall greyish blue humanoids with black hair. They became scientists and thinkers, experimenting on the worlds around them. One experiment led to the creation of a new species, the Psions. In a pivotal moment, billions of years ago, a Maltusian named Krona used time-bending technology to observe the beginning of the Universe. This experiment flooded the beginning of the Universe with entropy causing it "to be born old".
Feeling responsible for this, the evolved Maltusians relocated to the planet Oa (at "the center of the Universe") and became the Guardians. Their goal was simple: combat evil and create an orderly universe. And they acted quickly on that goal. During this period they also changed to their current appearance. They serve as the administrators of the Green Lantern Corps, an interstellar police force which patrols the universe.
Appa Ali Apsa