Kyle Rayner was an artist for the Daily Planet, recruited by the Green Lantern Corps after Abin Sur's death. The origin Rayner is given in the DC Animated Universe is a modified version of Hal Jordan's DC Comics origin. Kyle's original DC Animated Universe appearance was also more similar to Jordan than his own in the comics.
John Stewart was already a Green Lantern and reassigned to another space sector since Sector 2814 (which includes Earth) was already under the protection of Green Lantern Abin Sur. Following Abin Sur's demise at the hands of Sinestro, John would return to his home sector.
When Abin Sur crashed on Earth while fleeing Sinestro, he was mortally wounded. Abin sent his Power Ring to find his successor. The ring chose Kyle. No Hal Jordan :(
John Stewart was therefore sent to stand guard over Sector 2814, while Kyle Rayner was sent to Katma Tui for training.
Not long after John's homecoming, he would answer the fateful summons to join six other heroes in opposing the Imperium invasion. In the aftermath of that crisis, John readily agreed to Superman's suggestion that the seven heroes band together as the Justice League.
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