Ruthless Drule Warlord and friend of Prince Lotor.
Cossack the Terrible is a Drule warlord, first seen leading an attack on the planet Pollux, where he threatened Princess Romelle and the rest of it’s populous unless Princess Allura surrendered herself. Cossack was of course acting on behalf of Prince Lotor, and though Allura did indeed surrender herself to protect her cousin Romelle and the citizens of Pollux, thanks to the help of her father King Alfor’s, spirit Allura escaped, rejoining her comrades in the Voltron Force, and upon forming Voltron the group slayed the Octovore, a robeast which was acting as a ship to the prince of doom and Cossack. (Dinner and a Show)
But Cossack’s greatest claim to fame was leading an attack on the Galaxy Garrison on planet Earth which nearly succeeded, he secured the capture of the leaders of the Galaxy Alliance and Princess Allura, but thanks to Sven briefly retaking his old role as pilot of the Blue Lion, Cossack and Lotor’s attack was foiled by the (original) Voltron Force. (Who’s Flying Blue Lion?/Return of Sven)
Cossack would have many additional encounters with the Voltron Force, and one with the Voltron Vehicle Force (in the movie Voltron Fleet of Doom)
His relationship with other Drule is not much better then his relationship with members of the Galaxy Alliance though as Cossack was barely tolerated by King Zarkon, who allowed the warlord to have the forces of planet Doom fire on Stride’s Black Tiger ship for no reason other then the personal satisfaction Zarkon received from watching Cossack flee in terror when Stride fought back. Cossack and the witch Haggar are actually unlikely friends though, both feeling they are underappreciated and mistreated by Zarkon and Lotor, but Cossack is outright hated by Queen Merla who calls him a “bad influence” on Prince Lotor.
(Notes: While Cossack appears in many of the later episodes of Voltron, he never appeared in the original series GoLion, as all his appearances occurred in American exclusive episodes and the Fleet of Doom movie. If Cossack’s voice reminds you of a young King Zarkon who tells a lot of bad jokes, well both characters are voiced by Jack Angel, and to be fair some of Cossack’s jokes are funny! Cossack, though now much more buff, is a supporting villain in the series Voltron Force)
Voltron Fleet of Doom
To combat a seemingly unstoppable alliance between King Zarkon and Viceroy Throk, both Voltron Forces team up to combat the fleet of doom.