Justice League established the Green Lantern Corps in the DC Extended Universe, but it wasn't exactly clear which one appeared in the film. Now, a diligent fan seems to have figured out the character's identity.
The post, which comes from user StrandingDeath on Reddit, identifies the Green Lantern in question as Yalan Gur. The poster compares Gur's appearance in the comics with the character in the film, and the evidence seems pretty compelling.
Yalan Gur first appeared in 1991's Green Lantern #19. Gur served as the protector of Space Sector 2814 approximately two thousand years ago. The Guardians of the Universe removed the Yellow Impurity from Gur's ring, taking away its weakness. In the comics, power corrupted the character. He eventually died at the hands of humans when the Guardians made him vulnerable to wooden weapons
The character's fate in the film is much different from that of the comics. In the film, he dies during the battle with Steppenwolf during the film's "History Lesson" portion. His ring flies off after his death. Where his ring went is currently unknown, but that question may be answered by the upcoming Green Lantern Corps film.
The Green Lantern Corps movie is targeted for release in 2020. In theaters now, director Zack Snyder's Justice League stars Ben Affleck as Batman, Gal Gadot as Wonder Woman, Henry Cavill as Superman, Ezra Miller as The Flash, Ray Fisher as Cyborg, Jason Mamoa as Aquaman, Ciarán Hinds as Steppenwolf, Amy Adams as Lois Lane, Jeremy Irons as Alfred Pennyworth, Diane Lane as Martha Kent, J.K Simmons as Commissioner Gordon and Jesse Eisenberg as Lex Luthor.