Functionally immortal, Guardians resemble short (approximately 4 feet [120 cm] tall), large-headed, white-haired pale gray humanoids wearing red robes with their emblem, the Green Lantern symbol, on the chest. They possess vast knowledge, durability, awareness, flight, and psionic powers manifested through green plasma energy drawn from the most stable color of the emotional spectrum, green (willpower).
Prior to the creation of the Green Lantern Corps, the Guardians created the Manhunter Robots to keep order throughout the universe. They soon discovered the Manhunters were unable to understand the differences between good and evil, so they assembled the Lantern Corps and reprogrammed the Manhunters for other duties.
Centuries later, one of the Guardians, crash-landed on planet Earth, but was rescued by John Stewart. Shortly after, Hal Jordan arrived to help the Guardian, who in gratude offered Stewart membership in the Green Lantern Corps, which he accepted.
Two years later, Guardian Krallen contacted John Stewart for a mission that would take him back to his home planet: to protect the last survivor of planet Krypton, who had come under threat of the Supreme Kree Accuser Ronan. His task completed, Krallen relayed the news to the Galactic Confederacy to send a contingent to support Stewart in ensuring that Earth remains safe from future attacks. Later, Krallen allowed Stewart to be permanently reassigned to patrol the Sol System when he joined the Justice League.
When Earth was attacked by the Kree, Skrull and Shi'ar fleets, the Guardians sent over a hundred Green Lanterns, amongst them Hal Jordan, to aid in the planet's defense. Once the crisis was over and the negotiations for peace reached an end, the Guardians rearranged the Green Lanterns to patrol the sectors to ensure that any of the parties wouldn't try anything to break the agreements.
Background information Edit
The Guardians of the Universe are the male members of the Malthusans, possibly the oldest sentient species in the DC universe. After one of their own, Krona, witnessed the beginning of time, he somehow created the Antimatter Universe and introduced entropy into the universe. Feeling guilty, the male Malthusans emigrated to Oa and became the Guardians and dedicated themselves to combating evil in the universe, while their female counterparts became Zamorans. During their long history, the Guardians learned how to manipulate the collective embodiment of willpower, which is the energy used by the Lanterns. They were also responsible for imprisoning Parallax in the Central battery, splitting the Martians into two races, and guiding Kal-El's ship to Earth.
Following the Crisis on Infinite Earths, the Guardians decided to reunite with the Zamorans and produce a second generation of Guardians, who were to be raised in another sector of the Universe. Later, Hal Jordan, under the influence of Parallax, wiped out all the Guardians save the unorthodox Ganthet, who gave the last ring to Kyle Rayner. After Rayner evolved into Ion, he recharged the Central battery and created a new generation of Guardians, this time of mixed sex.