The Green Lantern Corps is widely known as DC’s band of space-cops, but they aren't the only peacekeeping force in the galaxy. First appearing in Michael Jan Friedman and Mike Collins' Darkstars #1, the Darkstars are another group of intergalactic space-cops who rose to prominence after Hal Jordan became Parallax, and the Green Lantern Corps was disbanded in the Post-Crisis DC Universe.
However, while the Green Lantern Corps is an altruistic no-killing band of heroes, the Darkstars don't exactly follow that same heroic path. Created by the Controllers, an offshoot of the Guardians of the Universe who seek to destroy evil rather than contain it like the Guardians, the Darkstars were corrupted after falling victim to loyalty issues and members who would act only to further their self-interests.
After realizing their first order keeping initiative N.E.M.O., the network for the Establishment and Maintenance of Order, was not direct enough, the Controllers devised a new plan that resulted in the creation of the Darkstars. This new initiative outfitted its members with the Exo-Mantle, a suit of armor that augmenting its wearer’s strength, speed and agility while also granting the ability to fly and project strong force fields that can be expanded to protect others.
The first Darkstar was Druu, who would become one of a thousand to carry the mantle. However, it wasn't until Ferrin Colos was tracking the supervillain Evil Star that the Darkstars arrived on Earth. Soon after the Central Power Battery would collapse with the fall of the Green Lantern Corps and the Darkstars would then begin to expand. This is when several members of their ranks began to act by their self-interest, with Huvah Jeddigar's actions being the most notable.
Jeddigar attempted to nurture a small universe that he hoped would help him expand his power, which lead to an investigation by Colos. After both of those Darkstars were sucked into a different universe, Donna Troy joined the Darkstars as Jeddigar’s hand-selected replacement prior to his death, and John Stewart also joined at the Controllers urging to keep an eye out for future corruption.
Eventually, the Controllers would abandon the Darkstars, believing they no longer followed their ideas, leaving only a handful of Darkstars active with inoperative Exo-Mantles. Darkseid’s son, Grayven, learned of this and began slaughtering the remaining Darkstars, forcing John Stewart and Donna Troy to gather the forces they had left and fight Grayven. Although the New God was defeated, the battle left JOhn severely injured, and Donn resigned to help him heal. Ultimately, all but three of the other Darkstars were killed.
The three remaining Darkstars would later be slain, only for the Darkstars to be revived as vessels of the demigoddess Lady Styx' will in Anderson Gabrych and Henry Flint's Omega Men, where they began slaughtering worlds to pave way for the coming of their lady.
After Flashpoint, both the Darkstars and the Controllers were depicted in a much darker light in Robert Venditti and Ethan Van Sciver's Hal Jordan and the Green Lanterns #42. The Controllers, seeking to re-establish order throughout the galaxy through Draconian style law enforcement, kidnapped the Guardians of the Universe to extract their genetic sequencing and create hybrid Controllers to expand their ranks. This was initially done to create a stronger hive mind that would allow them to control the new and improved Darkstars.
While the Controllers created the new Exo-Mantles to be easily controlled by them, the use of the 10th Metal in Scott Snyder, Greg Capullo, and Johnathon Glapion's Dark Knights: Metal #6 granted the Exo-Mantels sentience, and the suits rebelled against the controllers. This saw Green Lantern's Tomar-Tu and Guy Gardner join their ranks, though Guy would later overcome the suit through his considerable willpower.
All in all, the Darkstars are definitely a powerful team of intergalactic warriors. Whether as a group of heroes in the Post-Crisis DC Universe or villains in the New 52/Rebirth era, they are a force to be reckoned with.