While the DC Universe is filled with cosmic heroes who've turned its blackest nights into its brightest days, Hal Jordan is the most iconic and most accomplished hero to ever take up the mantle as a Green Lantern. Since he debuted in John Broome and Gil Kane's Showcase #22 in 1959, Hal's willpower has been shown time and again to vastly outmatch the will of any other Lantern to ever wear a Green ring.
While Hal is the most accomplished of all Lanterns and has the strongest will, it was only after he gave in to his fears -- and a cosmic parasite -- and became a villain and then sought redemption that he would down a path that led him to his most powerful form as the ghostly Spectre.
Armed with a standard issue Green Lantern Corps ring, Hal and his indomitable will are already a force to be reckoned with. Hal has accomplished some mind-blowing feats throughout his tenure as Green Lantern, like in Robert Venditti and Ethan Van Sciver's Hal Jordan and the Green Lantern Corps: Rebirth #1. In this issue, Hal is stranded on a desolate planet in Space Sector 563 without a ring and is seemingly fading away. Ruffling through his memories Hal manages enough willpower to forge his very own Green Lantern ring made from pure willpower, an event that sends a shockwave throughout the emotional spectrum and is felt by the other Green Lanterns of earth.
Aside from crafting a ring from pure will, Hal has regularly accomplished amazing feats with his ring constructs, like making living constructs. One example of this came in Geoff Johns, Eddie Barrows and Phillip Tan's Green Lantern #42, when Hal uses his ring to construct a virtual army of Green Lanterns to assist him in a battle with the Orange Lantern Larfleeze, as he once used his willpower to recreate Coast City, along with the constructs of his family and girlfriend.
Following the destruction of Coast City in Dan Jurgen's Superman #80 and the Green Lantern Corps' destruction in Ron Marz, Bill Willingham, Fred Haynes, and Darryl Banks' Emerald Twilight, Hal Jordan gave in to his fear and became to almighty villain Parallax after killing the Green Lanterns and absorbing the Central power battery. After wreaking havoc across the DC Universe as the villain, Hal/Parallax is eventually weakened and then killed by Green Arrow in Dan Jurgen's Zero Hour: Crisis in Time event. Eventually, Hal's actions would be rewritten as having been heavily influenced by Parallax, an ancienty evil entity that was essentially the embodiement of fear itself.
After a being released from purgatory as the result of a fallen angel trying to take power, Hal becomes the Spectre in Geoff Johns, Matthew Smith, and Christopher Jones' Day of Judgement #5.
Since DC's earliest age, the Spectre has been the chief agent of divine wrath in the DC Universe, with a functionally limiltess amount of power at his disposal. To wield all of that power justly, the Spectre also needs a human host, which Hal served as in the early '00s. However, Hal decided to alter the Spirit of Vengeance's mission to focus on redemption and began advising his fellow DC heroes in hopes of making up for his actions as Parallax.
As the true nature of Parallax was revealed, Hal was eventually be reborn again as a Green Lantern in Geoff Johns and Ethan Van Sciver's 2004 Green Lantern: Rebirth miniseries. While he's served in many different roles since then, Hal recently returned to the role in Grant Morrison, Liam Sharp, Steve Oliff and Steve Wands The Green Lantern: Season 2 #7 , when he breifly became the arbiter of universal justice once again.