As the last remaining member of the Green Lantern Corps, Kyle Rayner found himself alone in the universe in the '90s. Hal Jordan and the rest of the Corps were gone, only returning after a decade into Kyle's tenure. While Kyle was flying solo, however, he still had some notable encounters with Hal Jordan.
Kyle and Hal first met as enemies in Zero Hour: Crisis in Time #0, by Dan Jurgens, Jerry Ordway and Gregory Wright. By this point, Hal had become Parallax, attempting to use his powers to restart time and fix everything about his past. Hal and Kyle fought during Green Lantern #0, by Ron Marz and Darryl Banks. During their explosive battle, Kyle dispatched Parallax by destroying Oa.
Parallax returned to claim Kyle's Green Lantern ring during Green Lantern #63-64, by Ron Marz and Darryl Banks. At the end of this confrontation, Hal was convinced to leave out of shame for what he'd become. In Final Night #4, by Karl Kesel and Stuart Immonen, Hal sacrificed himself to reignite the sun, dying a hero. While Kyle had met the older, damaged Hal Jordan, he hadn't truly met Hal in his prime.
However, that changed It wasn't until Green Lantern #100, by Ron Marz and Darryl Banks, that Kyle met Hal Jordan at his heroic prime.
In this issue, Kyle was transported back in time to Hal Jordan's era. The two Green Lanterns worked with the rest of the Corps to defeat Sinestro, showing Kyle what it was like to be part of the Green Lantern Corps. By the end of this adventure, Kyle went back to the future, but Hal was accidentally sent with him.
This series of events began the "Emerald Knights" storyline, in Green Lantern #101-106, by Ron Marz, Jeff Johnson, Paul Pelletier, Anthony Williams and Scot Eaton. "Emerald Knights" reconnected Hal Jordan to his friends in the future, while he also came to terms with who he'd become. When Hal found out about Coast City's destruction and his transformation into Parallax, he was devastated.
As the hero he was, however, Hal overcame his grief in order to save a group of children from being hit by a train. Moving forward, Hal decided to settle in the future and build a new life. Hal met up with friends such as John Stewart, Guy Gardner, Carol Ferris and Tom Kalmaku. For a while, it seemed like Hal was returning to his heroic roots, fighting Kalibak and rejoining the JLA.
Of course, Kyle was initially jealous when Hal seemed to take his place among the rest of Earth's heroes. Fortunately, Batman reassured Kyle that he was the JLA's Green Lantern, settling things for Kyle. The Green Lanterns' happy coexistence didn't last, unfortunately. Parallax returned, demanding that Hal be sent back to his original time.
Apparently, when Parallax tried to restart time in Zero Hour #4, he detected an anomaly in the timestream, sending him to this particular point in history. After a long battle between Kyle, Hal and Parallax, Kyle reasoned that Hal should go back to his own time. The new Green Lantern reasoned that, since Hal sacrificed himself to save the planet during "Final Night," he would be needed in the future. With these words, Hal and Parallax went back to their respective times.
"Emerald Knights" left a significant impact upon both Kyle Rayner and Hal Jordan. For Kyle, going to Oa and visiting the Green Lantern Corps in its prime was a dream come true. This visit through time gave Kyle a true glimpse into the legacy which he was upholding at the time. Moreover, Kyle got to feel what it was like to work with his fellow Corpsmen. Kyle got the chance to truly understand the Hal Jordan of a bygone era. Rather than simply remembering Hal for his crimes as Parallax, Kyle got to know Hal for his heroism during the Silver Age.
At the same time, Hal got the opportunity to experience the future, for better or worse. Hal did get his memory wiped before he went back to the past. Yet, while he was in the future, Hal got the chance to redeem his legacy by reconnecting with others and facing his mistakes. Facing off against his older self, Hal reminded readers of a much simpler time, reconciling this with his inevitable downfall. When Hal returned to the past, he had left his mark on Kyle Rayner and the rest of DC's heroes, who saw him as a hero once more.
Ultimately, "Emerald Knights" also helped pave the way for Hal's return in Green Lantern: Rebirth #1, by Geoff Johns and Ethan van Sciver. By illustrating Hal's more heroic side and reconciling that with who he had become, "Emerald Knights" served as a reminder of who Hal Jordan truly was.