Parallax is a fictional character, a comic book supervillain in the DC Comics universe. Created by writer Ron Marz and artist Darryl Banks for Green Lantern (vol. 3) #48 (January 1994), Parallax was devised as the new supervillain identity for former Green Lantern protagonist Hal Jordan.
After further changes for the Hal Jordan character over the subsequent years (sacrificing his life in order to reignite Earth’s Sun in the 1996 crossover storyline Final Night, and Jordan’s soul subsequently became the newest host of the Spectre in the 1999 miniseries Day of Judgment), 2004's Green Lantern: Rebirth once again cast Jordan as a heroic Green Lantern and retconned Jordan's villainous career as the result of the influence of an alien parasite. Furthermore, with Parallax’s exposure, the Green Lantern Corps are no longer vulnerable to the yellow color.
In 1994, DC Comics decided to do away with Hal Jordan, who had been Earth’s Green Lantern since his first DC Comics appearance in 1959, hoping to replace him with a new, younger character Kyle Rayner, in order to attract new readers. The storyline began in Green Lantern (vol. 3) #48 (January 1994). Following the complete destruction of his home town Coast City by the villain Mongul, Hal Jordan descends into madness. Jordan went on a rampage, destroying the Green Lantern Corps, killing his friend Kilowog and all of the Guardians except for Ganthet.
Jordan was exonerated in the 2004/2005 miniseries Green Lantern: Rebirth, written by Geoff Johns, and pencilled by Ethan Van Sciver, in which it was revealed that Parallax was actually a demonic parasitic entity dating back to the dawn of time. The parasite was the sentient embodiment of fear, traveling from world to world and causing entire civilizations to destroy themselves out of paranoia.
The Guardians of the Universe imprisoned Parallax within the Central Power Battery on Oa using fear's opposite energy, willpower. Parallax had lain dormant for billions of years, its true nature hidden by the Guardians to prevent anyone from trying to free it. Being yellow in color, Parallax eventually came to be referred to as simply "the yellow impurity."
This was the reason why the rings were useless against the color yellow: Parallax weakened its power over the corresponding spectrum; hence, only someone with the willpower to overcome great fear could master the power ring. Thus, when recruiting new Green Lanterns, the Guardians were careful to look for recruits that were largely fearless. When the renegade Sinestro was later imprisoned in the Power Battery himself, his Qwardian yellow power ring tapped into Parallax's power and awakened it.
Since Sinestro hated Hal, Parallax chose Jordan as its tool to free itself. Parallax spent years influencing Jordan, causing him to experience increasing self-doubt as well as causing his hair to prematurely whiten at the temples. Parallax's control over Jordan became nearly complete with Jordan's grief over the destruction of Coast City, and it was Parallax who was responsible for Jordan's subsequent murderous activity, his apparent killing of Sinestro (actually a Parallax construct) and Jordan's destruction of the Central Power Battery, which allowed Parallax to graft itself onto Jordan's soul.
Despite Parallax’s seeming conquest of Jordan’s soul, Jordan’s heroic tendencies manages to manifest themselves enough for him to sacrifice his life in order to reignite Earth’s Sun in the Final Night crossover storyline. Jordan’s soul (with Parallax still grafted onto it) subsequently became the newest host of the Spectre, the vengeful spirit of God’s wrath in the 1999 miniseries Day of Judgment, written by Geoff Johns.
Since Parallax was gone from the Oan Power Battery, the final power ring conferred to Kyle Rayner did not have any weakness against yellow. The Spectre eventually ejected Parallax from Jordan's soul. The Spectre itself leaves to move onto the next human host. Ganthet guided Jordan's soul back to his own body, preserved after Jordan reignited the Sun during Final Night.
His soul and thoughts finally clear for the first time in years, Jordan was resurrected, again taking his place as a Green Lantern; even regaining some of his lost youth (evidenced by his hair becoming brown again).
Together, Jordan and Kyle Rayner, along with fellow Green Lanterns John Stewart, Guy Gardner and Kilowog (reborn thanks to Kyle) free Ganthet, whom Parallax had possessed after his expulsion from Jordan's soul. They imprisoned the parasite back in the Central Power Battery on Oa.
Despite this re-introduction of the "yellow impurity", which is now referred to as the Parallax Fear Anomaly, the power rings' weakness against yellow no longer applies, as experienced wielders are now able to consciously recognize its source, and overcome the fear associated with it. It is still, however, a considerable weakness for new GL recruits, who are ignorant of the impurity's nature or of how to combat it. During training, new recruits' rings may falter at times against yellow objects, and/or when a recruit is experiencing panic or fear, as seen with Soranik Natu.
Sinestro's Sinestro Corps captures Kyle Rayner with the intention of making him Parallax's new host. Sinestro reveals to Kyle the existence of Ion. Sinestro also informs him that Ion is actually an energy entity that needs a host, similar to Parallax, and it is now attached to Kyle's soul. Sinestro removes the Ion entity from Kyle, who is immediately taken over by Parallax. Parallax then clothes itself in a new uniform (which appears as a combination of Kyle's original Green Lantern costume and the costume Hal Jordan wore as Parallax) and returns to Qward with the Sinestro Corps.
Parallax becomes a herald of the reborn Anti-Monitor alongside Hank Henshaw, Superman-Prime and Sinestro himself. After the massacre of several Green Lanterns, Parallax leads an assault against Hal Jordan, John Stewart, and Guy Gardner, and brings them to Qward. The "Lost Lanterns" arrive to rescue the captured Lanterns. During the battle, Parallax murders Jack T. Chance after making him experience his repressed fear of his abusive family.
During his possession by Parallax, Kyle witnesses everything that Parallax does, including his murder of Jack. Kyle and Parallax confront each other in a room constructed by Kyle’s memories. Kyle changes into Ion and fights Parallax and later conjures a power ring and his original costume. After fighting Parallax for a while, Kyle loses. Kyle then stabs Parallax with a pencil and regains his self-worth when he sees a painting that his mother painted several years ago. Kyle walks into the painting and ends up in a field walking towards a bright, green star.
Later on Earth, Parallax is about to kill Hal’s brother and family when Hal confronts him just before his power ring runs out of power. Hal then uses the painting Kyle’s mother made in an attempt to expel Parallax from Kyle. Parallax then absorbs the painting and Hal into himself; this twofold increase of his powers upon combining the strength of both of his hosts turns him his natural yellow color and develop a costume that more closely resembles the one he wore when Jordan was his only host. Hal, in the form of a bright, green star, helps Kyle fight Parallax from within, and the two manage to escape from Parallax. Now in its original form, Parallax begins to attack Hal, Guy, John and Kyle. Ganthet and Sayd arrive and imprison Parallax within the Earth Lanterns' four Power Batteries.