The Sakaaran Mercenaries are supporting antagonists in both the 2014 Marvel film Guardians of the Galaxy and the 2019 Marvel film Avengers: Endgame. They serve as the elite military force for both the Kree fanatic Ronan the Accuser and Thanos.
Guardians of the Galaxy
Since the Sakaarans were considered close friends with the Kree, the Sakaaran mercenaries were hired by Ronan to aid him in his goals of destroying the planet Xandar as he finds the Kree-Xandar treaty to be an embarrassment for his Kree belief. Striking a deal with the infamous warlord Thanos, Ronan sends over Gamora and Korath the Pursuer to steal the Orb (containing an Infinity Stone) so that Thanos would use it to destroy Xandar for Ronan.
However, the orb was stolen by Peter Quill (the protagonist of the film), who ends up being jailed alongside Gamora, Drax, Rocket Raccoon and Groot. Ronan eventually learned that Gamora actually intends to deliver the Orb to the Collector, so he summons Nebula and the Sakaaran mercenaries to track her down and kill her. They tracked Gamora down to a prison, where they learned that Gamora has already escaped with the Orb and intending to deliver to the Collector as promised. As such, Ronan angrily orders the Sakaarn mercenaries to burn down the prison, killing all officers and inmates in the process.
However, Ronan was able to track down Gamora thanks to a message from Drax, who intends to kill him for the death of his family. As Ronan easily defeats Drax, Nebula managed to steal the Orb. With the Orb finally in his place, rather than delivering it to Thanos, Ronan instead fuses the Stone with his hammer, intending to destroy Xandar himself before killing Thanos.
As Ronan sets his ship to invade Xandar, he gets the Sakaaran mercenaries to fire up the ship's weapons systems against the planet; even several Sakaaran pilots resorted to suicide attacks to take down their enemies. Fortunately, Peter and his friends brought in the Yondu Ravager Clan (led by Yondu Udonta) and the Nova Corps to help fight off all of the Sakaaran mercenaries to their deaths. Despite the losses of Korath and the mercenaries, as well as the departure of Nebula, Ronan turned the tide of the battle by using the Stone to defeat the Ravagers and Nova Corps armada, though the Guardians managed to retrieve the Stone and use it to kill Ronan for good.
The Sakaaran Mercenaries appeared briefly, numbering in thousands as Thanos brings his armies of the Black Order, Chitauri soldiers, Outriders and Leviathans after learning that the Avengers went back in time to retrieve the Infinty Stones and used them to undo the massacre of half of the universe' populace that his future self committed. Deciding now that he would have to use the Stones to wipe out all life in the universe and recreate it under his own image, Thanos sets his armies to invade and destroy Earth. Fortunately, several revived heroes come to the rescue while Iron Man sacrifices himself to use the Stones to erase Thanos and his forces from existence. As such, the Sakaaran mercenaries fade away from existence along with Thanos and his other forces.
A Maskless Sakaaran was voiced by James Gunn, who directed Guardians of the Galaxy.