Once thought to be merely an honorary title in the Green Lantern Corps, Ion is in fact the symbiotic willpower entity birthed from the green of the emotional spectrum. Its existence was kept a secret from the Green Lantern Corps since their inception, and it resided in the central power battery to keep Parallax in check.
Only after the destruction of the Central Power Battery were both Ion and Parallax set free. Ion wandered the cosmos for a time, and eventually was reined in by what was then the only surviving green lantern ring, that of Kyle Rayner.
Kyle Rayner served as its host briefly, and noted that his powerbase was so greatly expanded, he didn't need a power battery or power ring to manifest the emerald energy.
Unlike Parallax, Ion does not influence the users' actions.
Power of Ion
The creature seemed to first become one with Rayner when he lost his girlfriend Alex. He unconsciously expelled all his feelings of rage from himself, which took form as Oblivion, a being of energy that eventually manifested itself in the form of one of Kyle's childhood nightmares. Kyle defeated Oblivion in the Circle of Fire storyline, and was able to tap into that power. However, his power seemed to be getting stronger without his knowing it. It would be logical to assume that Ion's power began affecting him around this time.
As Ion, Kyle was bestowed with god-like powers. He was able to project himself in dozens of different places at the same time and had a limitless amount of energy.
Large contributions from the creature included giving Kyle the power to recharge the Central Battery on Oa. With the power he had, he formed new Guardians whom Ganthet looked after as he taught them the protocols and responsibilities of being members of the Guardians of the Universe. He used all the extra power he had to fully recharge the battery, thus allowing for the eventual return of the Green Lantern Corps. Not long after the rebirth of Hal Jordan, the Corps began being active once again due in large part to Kyle and the creature's symbiotic relationship.
After a period of time as a regulation Green Lantern, Kyle was bestowed with the power of Ion once again and was labeled as the true Torchbearer for the Guardians. This new manifestation of Ion is not as strong as the first one which affected Kyle, due to the fact that he relinquished much of his power to rebuild the Corps and bring back the Guardians. Currently however, the Ion creature was forcefully extracted from Kyle and imprisoned on Qward by the newly established Sinestro Corps. Upon expelling Ion from Rayner, Sinestro himself forced Kyle into the domain of Parallax, who invaded his body and forcefully bonded with him. 
Ion was then held in captivity by the Anti-Monitor, the cosmic entity attempting to draw Ion's power to himself. Eventually a group of "Lost Lanterns" freed Ion from confinement on Qward and returned him back to the positive Universe and to Oa.
In Green Lantern #54 a mysterious figure travels to Daxam's sun, which was transformed yellow by Sodam Yat with the Ion power. Yat was in the center of the sun in a petrified state, while the Ion energies kept the sun yellow. The figure states that while the Blackest Night prophecy said that Yat would be the last Green Lantern; the prophecy was written under the assumption that the universe would end. However, the universe did not end and that as long as he protects the universe it would not end. He compliments Yat on his role as the host to Ion, but tells him that turning the sun yellow and thus giving his people powers made them dangerous due to their xenophobia. He then rips Ion out of Yat, which frees him from his petrified form and sends him crashing down to Daxam. With Ion gone the sun returns to its original red color and the Daxamites lose their super powers. The figure imprisons Ion next to Parallax.
- Willpower Induction: Ion has practically infinite Willpower-casting powers.
- Connection: It can make a connection with someone's body when they feel have given to incredible willpower or have distanced themselves from their more complex emotions.
- Time Manipulation: Ability to control time
- Reality Manipulation: Ability to control reality.
- Willpower-Induced Energy Manipulation: As the embodiment of willpower, Ion can control, manipulate and generate green energy derived from the emotional spectrum of the universe, which comprises all the willpower of all sentients in the universe. All powers similar to a Green Lantern Corps Power Ring and the Starheart.
- Immortality: As an entity based upon an emotional concept, Ion is, for all intents and purposes, unending.
- Ion was revealed as being that had merged with Kyle Rayner in Infinite Crisis Special: Rann-Thanagar War #1. It first appeared as a separate creature in Green Lantern: Sinestro Corps Special #1.
- 44 Appearances of Ion (New Earth)
- 9 Images featuring Ion (New Earth)
- Quotations by or about Ion (New Earth)
- Character Gallery: Ion (New Earth)