The Eidelons are a pacifistic race who inhabited the planet Arnessk and Qujaga. They possess a unique ability tied to their physiology. They have a special gland that vibrates to create an energy field that "has a calming effect on individuals, allowing them to see reason". Using this empathic ability, the ancient Eidelons and later their descendants could convince a foe to follow a peaceful path to their objectives.
Unable by themselves to keep all the subjects in their influence peaceful, the Eidelons sought out a species to serve as a guard, a race no one had quarrel with, a force to ensure harmony prevailed once negotiations had finished. The Eidelons took great care to choose a species no one had met before. They found primitive humans, barely clothed, far removed on the galaxy's outer spiral. They brought some of them back to their homeworld of Arnessk and employed genetic engineering to enhance them. This new species became known as the Sebaceans and they became the Eidelons' trusted acolytes. They took on the name of Peacekeepers due to their function.
12,000 cycles prior to John Crichton's arrival in the Uncharted Territories, Arnessk became uninhabitable, and the Eidelons fled to other planets. Some remained in their Arnessk temple, however, and entered suspended animation of a sort, causing their temple to disappear from time. The Peacekeepers attempted to carry on once the Eidelons vanished. However, lacking the Eidelons' mediation abilities, they kept the peace the only way they could - at the muzzle of a gun. When the three probes that comprised the Darnaz Triangle were reactivated by Crichton, Chiana and Jool, Arnessk became habitable again and the temple reappeared.
In Farscape: The Peacekeeper Wars, the last surviving Eidelon colony is discovered hidden on Qujaga, the water planet where Moya is healing. During the time they have been away from Arnessk, however, they lost their empathic abilities. Crichton takes a pair of the Eidelons to meet their ancestors in the hope they can be taught the power once more. However, the Scarrans appear to eradicate all of the ancient Eidelons.
The new Eidelon colony does eventually regain its powers of mediation through Stark, who gains the knowledge as he crosses over one of the dying ancestors, and he in turn passes the ability on to one of the colony. The event also leaves Stark's mind at peace, no longer filled with the pain of others, and his power to cross spirits over is gone.
- The debate over the spelling of "Eidelon" may be easy to explain. There is an actual English word "eidolon", which comes from the Greek eidos, for the term for a person's "astral double" or ghost. Readers may be more familiar with the out-of-body-experience phenomenon in which a spiritual body, i.e. the eidolon, travels independent of the physical body. The use of this base word for the species may be a nod to the fact that their spirits could be captured as Stark was forced by John Crichton to do on a dying Eidelon.