The series focuses on the adventures of Hal Jordan, the Green Lantern of Sector 2814, and his partner Kilowog. Hal Jordan travels to "Frontier Space" the region of space at the edge of the Guardians' territory, where Green Lanterns are being picked off by the Red Lanterns. Atrocitus, their leader, wants revenge for the destruction of his world by the Manhunters, the now-decommissioned android enforcers of the Guardians. After defeating Atrocitus, Hal and Kilowog adopt Razer, a maverick Red Lantern into their fold. Their next great threat is the Anti-Monitor, who seeks to literally consume the Universe.
The show was planned out for 4 seasons.
- Hal Jordan/Green Lantern (voiced by Josh Keaton) – The main protagonist, Hal Jordan is the first human to become a Green Lantern, and is considered one of the best. He is an almost fearless and skilled Lantern. He has a history of disobeying orders and disregarding rules to achieve success. His superiors see him as a loose cannon, but they are willing to overlook his transgressions due to his skill and accomplishments. At the start of the second half of Season 1, he was replaced by Guy Gardner as the Green Lantern of Earth, but was promoted to Honor Guard Corps for his victory over the Red Lanterns.
- Kilowog (voiced by Kevin Michael Richardson) – A veteran Green Lantern, Kilowog is a close friend of Hal and is in charge of training new Green Lantern recruits. Kilowog accompanies Hal in Frontier Space. He is a member of the Honor Guard, and is less willing to abandon the rules of the Corps. Kilowog is often skeptical of Hal's actions, but he is completely loyal to Hal.
- Aya (voiced by Grey DeLisle) – The Interceptor's AI, Aya is an strong AI and artificial consciousness created by Scar as an empathetic alternative to the Manhunters. Scar created an extremely advanced computer, but was not satisfied with its lack of social intelligence, so infused it with a fragment of an entity inside the Green Lanterns' Central Battery. However, due to this Aya developed a consciousness with her curiosity and free will, leading Aya to transfer data without Scar's permission. When caught, Aya asked Scar why Scar was not complying with the other guardians. This led to a brief power struggle inside Scar's lab. The power struggle resulted in Aya's memory being wiped by Scar and Aya being installed into the Intercepter as its AI. Able to interface with other machines, Aya's consciousness resurfaces as she begins to consider herself a Green Lantern while developing feelings for Razer. But the episode "Cold Fury", after having her heart broken, Aya shuts down her emotions in order to destroy the Anti-Monitor by removing his head from his body so she can attach herself to it. Afterwards, wielding the Anti-Monitor body and overcome by its coercive persuasion and declaring that her former team cares nothing for her and her kind, the emotionless Aya takes control over the Manhunters before departing to travel back to the Big Bang so that the universe develops without emotional beings. Her "clothing" changes into black, a likely allusion to the Black Lantern Corps. However, as a genuine living being, Aya was never able to completely seal off her emotions and critically wounding Razer when his "unsuccessful" attack during Jordan's own use of the fight-and-talk strategy cured her of the Anti-Monitor body's coercive persuasion. With the Manhunters still a threat, as well as each possessing a copy of her coding, Aya releases a virus to wipe all versions of the Aya program from existence, including herself. Razer begs her not to leave him, but she responds that she will always be with him before disappearing.
- Razer (voiced by Jason Spisak) – A reformed Red Lantern who is exclusive to the series. Razer was a follower of Atrocitus but began to question him, and eventually turned against the other Red Lanterns after they placed a bomb on a colony planet. They forced Razer to activate it to prove his loyalty, subsequently destroying the planet. The guilt-ridden Razer sought out Hal and tried to provoke him into killing him as penance. Hal, however, took him prisoner. After Razer proved himself (and discovered Kilowog managed to save most of the colonists), he was invited to join the team and make up for his past actions, now fueling his Red Power Ring with the rage he feels towards Atrocitus for turning him into a murderer. Razer has, over the course of the series, fallen in love with Aya, who based her physical appearance on his dead wife Ilana. He confessed his love for her at the end of "Loss", but took it back in "Cold Fury", saying that he only felt love because she looked like Ilana, although the truthfulness of this is unclear. At the end of "Dark Matter", Razer refuses to believe that Aya is truly gone, having made that mistake once before, and vows to scour the galaxy for as long as it takes to find her. As he flies off into space, a Blue Lantern ring appears and flies after him, implying that Razer, now filled with hope rather than rage, will become a Blue Lantern. A character design sketch from a proposed new season of episodes shows Razer dressed as a Blue Lantern and saying, "Hello, Aya, it's good to see you again."
Guardians of the Universe:
- Ganthet (voiced by Ian Abercrombie)
- Appa Ali Apsa (voiced by Brian George)
- Sayd (voiced by Susan Blakeslee)
- Scar (voiced by Sarah Douglas)
Green Lantern Corps:
- Mogo (voiced by Kevin Michael Richardson) – A sentient planet that imprisoned criminals on its surface for many years before becoming a Green Lantern.
- Salaak (voiced by Tom Kenny) – A multi-armed Green Lantern senior administrator who appears in the first season finale, defending the Guardians from the Red Lantern invasion. He is visibly upset when he discovers that the Guardians have been withholding information from the Corps. Salaak appears in the final episode of the series, acting as the battlefield coordinator in the fight against the Manhunters.
- Ch'p – Ch'p appears as a new recruit of the Green Lanterns pitted against Hal Jordan as part of a bet. In a convincing display of skill, the Green Lantern squirrel easily defeats Jordan, winning the bet for his trainer, Kilowog. He later assists Hal in rescuing Aya from the Guardians' labs. Ch'p appears again as a squadron leader during the Battle of Ranx. He also participates in the final battle against the Manhunters in the series finale. Ch'p is not mentioned by name nor does he have any spoken dialogue. He is referred to in the series as "Sector Recruit 1014", which is consistent with the character's sector assignment in the comic books.
- Tomar-Re (voiced by Jeff Bennett) – Tomar-Re is a member of the Green Lantern Honor Guard, who teams with Hal to investigate the Manhunter threat. He later appears at the Battle of Ranx, leading one of the Green Lantern squadrons.
- Guy Gardner (voiced by Diedrich Bader) – Hal's replacement as the Sector Lantern of 2814 after Hal's victory over the Red Lantern Corps and promotion to the Corps Honor Guard. Quickly promoted to Honor Guard duty, Guy is placed in charge of the Corps during the Battle of Ranx, much to Hal's chagrin. He states that after being promoted, he was replaced by John Stewart as the Green Lantern of Earth. Guy also leads the Corps against Aya's Manhunters in the season 1 finale.
- John Stewart (voiced by Phil LaMarr) - Guy's replacement as the Sector Lantern of 2814, when he learned Hal committed a crime and went rogue, he hunted him down, only to work with him in the mid finale when they discover Sinestro framed Jordan.
- Sinestro (voiced by Ron Perlman) – Considered one of the greatest, though unconventional in his tactics, Green Lanterns, he is Hal Jordan's idol and mentor. He has shown to be willing to kill his enemies, in violation of Green Lantern protocols.
- Chaselon (voiced by Tom Kenny) – The crystalline Green Lantern is first seen in the episode "Reboot", where he is assigned to watch over the lab where Aya is being dissected. He is distracted by Hal Jordan while Ch'p recovers Aya's memory core. Later, Chaselon serves in Guy Gardner's squadron at the Battle of Ranx, alongside Larvox, and later fights against the Manhunters in the season 1 finale. Chaselon is characterized as naive and somewhat lonely, admitting to Hal that he has few friends on Oa.
- Iolande (voiced by Tara Strong) – Queen of the planet Betrassus. When Hal and Kilowog arrived on her planet to recruit its resident Green Lantern, Dulock, to fight the Red Lanterns, one of her generals attempted to force her hand in marriage, which Dulock openly challenged. When her brother, Ragnar, murdered Dulock to obtain his ring, it instead passed to Iolande, who resolved to remain her planet's queen and its protector.
Red Lantern Corps:
- Atrocitus (voiced by Jonathan Adams) – The (former) leader of the Red Lantern Corps. Due to his planet's destruction, the power of the Red Ring and ruthless crusade of revenge against the Guardians and the Green Lantern Corps, Atrocitus never found true happiness as he was willing to destroy other worlds no matter the cost.
- Zilius Zox (voiced by Tom Kenny) – A sycophant who is almost never far from Atrocitus's side, constantly offering him praise. After Atrocitus was arrested, Zox became the new leader of the Red Lanterns.
- Bleez (voiced by Grey DeLisle) – The only female Red Lantern depicted, Bleez comes from a winged race and prefers to rely on her own wings to fly while in-atmosphere, rather than her Red Power Ring.
- Veon (voiced by Jason Spisak) – A one-eyed Red Lantern who apparently possesses some measure of psychic ability.
Skallox (voiced by Kevin Michael Richardson) – A hulking, brutish Red Lantern with an ongoing rivalry against Kilowog, his physical equal.
- Cleric Loran (voiced by Corey Burton) – An eyeless, armored, slug-like alien of an unknown species who is exclusive to the series. Loran does not appear to possess a Power Ring, but maintains a Chapel dedicated to Atrocitus on the Red Lantern's base, the Shard. Loran, along with the Red Lantern Corps, venerates Atrocitus as a prophet and visionary, calling Atrocitus' rage "holy", and quoting passages from the Book of Rage (an object similar to the Book of Parallax, the Book of Oa, and the Book of the Black) like scripture.
- Ragnar (voiced by Will Friedle) – Ragnar is a character that exists in the mainstream of DC Comics, but only becomes a Red Lantern in Green Lantern: The Animated Series. He was responsible for the death of his planet's resident Green Lantern, Duloc, in hopes that his ring would choose him. After failing to become a Green Lantern and seeing his sister (Queen Iolande) chosen in his place, his great rage at failing to gain the power of a green ring brings him to the Red Lanterns.
Blue Lantern Corps:
- Saint Walker (voiced by Phil Morris) – The first Blue Lantern in the universe.
- Brother Warth: (voiced by Brian George) – The second Blue Lantern whose appearance is that of an elephant.
- Carol Ferris (voiced by Jennifer Hale) – Hal Jordan's love interest and Vice President at Ferris Aircraft. In "...In Love and War", she learns Hal Jordan is a Green Lantern. In "New Guy", she breaks up with Hal after she realizes that his duties to the Green Lantern Corp complicated their relationship. In "Love Is a Battlefield" Carol is brought back to Zamaron to be the champion of Love and fight Atrocitus who is the champion of Hate. Her battle with Atrocitus is tough and she realizes that she can use her power ring to call her loved one to aid her. Hal comes through the star portal to help Carol and together they defeat Atrocitus. At the end of the episode, Carol decided to keep her ring to honor Gi'ata and also renews her relationship with Hal.
- Queen Aga'po (voiced by Grey DeLisle) – The queen of Zamaron and leader of the Star Sapphires. She and her Corps use the power of Love to help couples to be together.
- Gi'ata (voiced by Jennifer Hale) – The niece of Queen Aga'po. She thought Love was just a way to help people became happy by bringing loved ones together. In "Love and War" she falls in love with Hal even though Hal loves Carol. Carol tells Gi'ata how Love is supposed to be and how the feeling really means. With that, Gi'ata taught her people what true love really is by the end of the episode. In "Homecoming" she helped Hal and Razor get to the destination to save Oa by being transported to their loved ones. In "Love is a Battlefield" Aya going viral attacks Zamaron believing that Love is the most destructive emotion of all. Gi'ata points out that it is not evil as she was taught that Love really means which she was taught by her teacher. Aya brings Carol back to Zamaron to know if it is true, than decided a trial between Love and Hate by bringing Atrocitus to represent Hate and Carol represent Love as Gi'ata gives Carol her sapphire ring and Aya gives Atrocitus his red power ring. In the battle with Carol and Atrocitus, Carol calls Hal for help as Hal enters the star portal to help Carol. In the battle, Atrocitus use his red flame blast to kill Hal, but Gi'ata flew in to intercept Atrocitus's attack, mortally wounding her. When the battle ended, Hal told her that she shouldn't have sacrificed herself, but she responded that there is no greater honor than to protect love as noble as theirs.. Queen Aga'po tells Hal, Carol, Razer, and Kilowog that her niece did not die in vain, but to protect the true meaning of love and will be honored as the greatest Star Sapphire of Zamaron, with Carol saying they will remember Gi'ata in their hearts as a true hero.
- Galia (voiced by Vanessa Marshall) - Kilowog met her on her home planet. She reminds him of his wife seeing how their species look alike. In "Fear Itself", Kilowog helps her people fight their enemies who turns out not to be hostile but to help get rid of the yellow crystals that are poisonous. In "Love and War", Galia was brought to Zamaron by Queen Aga'po to become a Star Sapphire as a way to capture Kilowog, however, in "Homecoming" and "Love Is a Battlefield" she is not seen among the Corps suggesting that she may have been released from her duties to the Star Sapphires.
Orange Lantern Corps:
- Larfleeze (voiced by Dee Bradley Baker) – The sole member of the Orange Lantern Corps and a greedy criminal, hence his powers.
- Glomulus – A construct of the Orange Light.
- Hal Jordon (temporary, under the coercive persuasion of the orange lantern battery) - First coming to "borrow" then openly steal the orange lantern battery, Jordon turns orange when his greed allows the battery to overcome him. The increasingly botched heist degenerates into a physical fight which Jordon "wins". His companions realize that the orange lantern battery's coercive persuasion is based on preying on it's victim's greed, and make a deal with Larfleeze for his help in depriving Jordon of the orange lantern battery in exchange for departing and returning the battery to Larfleeze. Instead of using coercive persuasion of their own, Jordon's companions successfully use a fight-and-talk strategy to get Jordon to abandon the battery of his own free will. Jordon turns back to green again and tells Larfleeze that their purpose in coming there became to steal, but that they were wrong. Larfleeze regains his battery, and Jordon and his companions leave more-or-less amicably.
- Anti-Monitor (voiced by Tom Kenny) – An enormous robot created by a renegade Guardian, the Anti-Monitor has an insatiable hunger and feeds on literally everything. After going rogue upon creation, his creator banished it to an alternate dimension, but this only caused that dimension to be fed on. Eventually the Anti-Monitor returned to his own dimension, resurrected the Manhunters, and began wreaking havoc, thus becoming the second season's main antagonist for the first half. However, in "Cold Fury", the Anti-Monitor's head was separated from his body by Aya as she took it for her use. Eventually, she finished the job to obtain an item needed for her agenda.
- Manhunters (voiced by Josh Keaton) – Emotionless robots created by the Guardians to serve as soldiers of the Green Lantern Corps. However, they were given imperfect programming which caused them to determine that since crime is caused by emotional responses, all beings with emotions must be evil. They wiped out an entire sector before the Guardians stopped them, and the Red Lantern Corps was formed to avenge this genocide. The Manhunters were revived by the Anti-Monitor in the second half of the season. After Aya destroys the Anti-Monitor, she names herself the queen of the Manhunters and copied her data into them.
- LANOS (voiced by Brian George) – Lanos is an artificial intelligence that replaced Aya on the Intercepter after she was removed for dissection. Returns for two episodes after Aya becomes the Aya Monitor and sacrifices himself to save the crew. Known for an annoyingly cheerful personality and his tendency to "fly like a madman" while neglecting the use of inertial dampeners. He sacrificed himself to save the others from Aya by ramming the Intercepter into her and sending them both through hyperspace. Kilowog nicknamed LANOS "LAME-O" (a pun on LANOS' real name).
- Atrocitus (voiced by Jonathan Adams) – The (former) leader of the Red Lantern Corps. Due to his planet's destruction, the power of the Red Ring and ruthless crusade of revenge against the Guardians and the Green Lantern Corps, Atrocitus never found true happiness as he was willing to destroy other worlds no matter the cost. He is the main antagonist in the first half of Season 1.
- Anti-Monitor (voiced by Tom Kenny) – An enormous robot created by a renegade Guardian, the Anti-Monitor has an insatiable hunger and feeds on literally everything. After going rogue upon creation, his creator banished it to an alternate dimension, but this only caused that dimension to be fed on. Eventually the Anti-Monitor returned to his own dimension, resurrected the Manhunters, and began wreaking havoc, thus becoming the second season's main antagonist for the first half. However, in "Cold Fury", the Anti-Monitor's head was separated from his body by Aya as she took it for her use. Eventually, she finished the job to obtain an item needed for her agenda. He is the main antagonist of the second half of Season 1, until he was replaced by Aya.
- Aya Monitor (voiced by Grey DeLisle) – In the episode "Cold Fury", after having her heart broken, Aya shuts down her emotions in order to destroy the Anti-Monitor by removing his head from his body so she can attach herself to it. Afterwards, wielding the Anti-Monitor body and overcome by its coercive persuasion and declaring that her former team cares nothing for her and her kind, the emotionless Aya takes control over the Manhunters before departing to travel back to the Big Bang so that the universe develops without emotional beings. Her "clothing" changes into black, a likely allusion to the Black Lantern Corps. She is the main antagonist after Anti-Monitor in the second half of Season 1. However, as a genuine living being, Aya was never able to completely seal off her emotions and critically wounding Razer when his "unsuccessful" attack during Jordan's own use of the fight-and-talk strategy cured her of the Anti-Monitor body's coercive persuasion. With the Manhunters still a threat, as well as each possessing a copy of her coding, Aya releases a virus to wipe all versions of the Aya program from existence, including herself. Razer begs her not to leave him, but she responds that she will always be with him before disappearing.
- Sinestro (voiced by Ron Perlman) – Considered one of the greatest, though unconventional in his tactics, Green Lanterns, he is Hal Jordan's idol and mentor. He has shown to be willing to kill his enemies, in violation of Green Lantern protocols. He becomes the main antagonist of the first half of Season 2, having framed Hal Jordan for destroying the main battery, as he plans to find the Yellow Qwardian Battery to control the planets..
- Blackhand (voiced by Maurice LaMarche) - He is the main antagonist of the second half of Season 2. His goal is to control the dead.
- Hector Hammond (voiced by Grant Moninger) - The main antagonist of the first half of Season 3. a delusional scientist who gained an enormous head from absorbing Ganthat's power, his goal is to recreate the universe in his image.
- Krono (voiced by Ike Amadi) - The main antagonist of the second half of Season 3. ??? goal is to ???
- Power Ring (voiced by Paul St. Peter) - The main antagonist of the first half of the final season. ??? goal is to ???
- ??? (voiced by ???) - The main antagonist of the second half of the final season. ??? goal is to ???