Mostly on here for his long history with Green Lantern going all the way back to Alan Scott, Sportsmaster was an athlete who was banned from professional sports forever for cheating. Now he uses his skills as a criminal, and hitman. And well known for his villain role in Young Justice.
9. Carol Farris
Once Hal Jordan's girlfriend/boss and owner of Ferris Air, where Jordan tested fighter planes, Carol Ferris became a Star Sapphire. Unlike a Green Lantern ring which runs on Will, a Sapphire ring runs on Love. Which at the time was for Hal Jordan, but when she put the ring on she became a villain being blinded by all the lies Hal had told her throughout the years while hiding his Green Lantern alter-ego. But now that she knows the truth and has control she has been a hero for the past few years, usually fighting along side her ex. Other than that Carol's uniform has been roasted for being useless and way to revealing for years. Look for has Star Sapphire in Green Lantern: The Animated Series.
Star Sapphire Oath: For hearts long lost and full of fright, For those alone in Blackest Night. Accept our ring and join our fight, love conquers all with violet light!
Larfleeze or Agent Orange is the Orange Lantern. Able to create his own lantern corps out of the people he has killed postmortem, Larfleeze is a force to be reckoned with. With the power of Avarice on his side he will do anything to keep his lantern to himself. At most points he has proven more powerful than Hal Jordan, being the only Orange Lantern to use it's power. He is also in Green Lantern: The Animated Series.
Orange Lantern Oath: What's mine is mine, What's yours is yours, Until I make yours mine. With orange light, It's all mine!
Ever heard of the massacre of Sector 666? Well before the Guardians of The Universe created the Green Lantern Corp, there were the Manhunters. Robots doing what Green Lanterns would soon do, only without out thought or remorse. Because of their want to make the galaxy a better place they destroyed millions of lives, trying to get all the bad out of the world, which meant killing any living being. After destroying an entire sector (Sector 666), only five beings remained, which were soon called the Five Inversions, alien terrorists on a mission for revenge against the Guardians. Atrocitus was one of those five, he became the first Red Lantern after Christening his lantern in the blood of a fellow Inversion. Able to spit acid fire out of his mouth, and use his intense rage to tear anyone to shreads, Atrocitus gives any Green Lantern trouble.
Fun Fact: Atrocitus was the one who injured Abin Sur on his way back to Oa. So indirectly Atrocitus created one of his greatest foes...Hal Jordan.
Red Lantern Oath: With blood and rage of crimson red, Ripped from a corpse so freshly dead. Together with our hellish hate, We'll burn you all--That is your fate!
Once a scientist for the Guardians of The Universe, Krona had a thirst for knowledge and intergalactic order. He even tried to stop his fellow Maltusians into becoming the Guardians of The Universe. After being attacked by the Manhunters, he reprogrammed them to commit the massacre of Sector 666. During one of his out of the boxy experiments, an explosion happened creating the Multiverse and giving birth to Monitor and Anti-Monitor. Krona returned after thought dead, harbinger of Brightest Day trying to capture all the Emotional Entities. Soon after Hal Jordan killed him with a burst of Will, and his body was given to Atrocitus after a previous agreement with the Guardians.
Harbinger of the Blackest Night and leader of the Black Lantern Corp, Nekron can give and take life as he pleases. His origin is fuzzy, but he has been said to be one of the first Guardians created out of the darkness of the universe. Because of his power he searched for the Entity of Light, the White Lantern. During Blackest Night, the heroes of DC became the White Lantern Corp to defeat Nekron and stop him from killing every living being on this plane.
Black Lantern Oath: The blackest night falls from the skies, The darkness grows as all light dies. We crave your hearts and your demise, by my black hand the dead shall rise.
4. Black Hand
You'd think Nekron would be worse than Black Hand but that isn't entirely the case with Black Hands insane mind and will to kill anything that comes in his way. William Hand after his suicide rose from the dead as the Black Hand, and gained the ability to syphon the life force out of his victims. He is one of Hal Jordan's oldest foes. During Blackest Night, Black Hand was Nekron's tether to this world. Hal creates the White Lantern Corps, and defeats Hand giving the heroes a chance to finally defeat Nekron. Now he is apart of the Indigo Tribe, after one of the Lanterns translated something he said as he was captured to "Help Me".
The living embodiment of Fear, the Guardians trapped Parallax inside a box which was soon discovered by Larfleeze while he was also finding the Orange Lantern Power Core. During Larfleeze's discovery Parallax was set loose, and all who tried and stop him were killed instantly. Soon though the Guardians had him placed inside the Green Lantern Power Core on Oa, which in turn gave the Green Lantern their weakness to the color yellow and their deadliest emotion. Parallax has taken over Hal Jordan and Kyle Rayner, fellow earth Green Lantern's for a time.
Emotionless and flawed robots created by the Guardians of The Galaxy to maintain peace in the Galaxy before the Guardians created the Green Lantern Corps. Harbingers of Massacre of Sector 666, and murderers of millions the Guardians soon realized that their creations were more trouble than good, and so came the Green Lanterns, whom were the ones to exile the rest of the Manhunters. They are the Guardians biggest mistake, and the Green Lantern Corps has been cleaning up their mess ever since they were created.
Once thought of the greatest green lantern of them all, but then exiled after he abused his power. Sinestro came across the Yellow Lantern, which used fear as it's weapon and was the complete opposite of the Green Lanterns. With many other Yellow Lanterns to do his bidding like Arkillo and Slushhh, Sinestro is a force to be reckoned with. Not only that but he was once Hal Jordan's and the Green Lantern's ally so there is always some bitterness when the three fight. Sinestro is in the first position for that reason, Sinestro is always there to get in the way of any Green Lantern and will do anything it takes to get what he wants. Anything.