Zarkon was the ruthless and overbearing ruler of the Galra Empire and had been ruling into the present day for 10,000 years. He was once the a Paladin of Voltronas The pilot of the Black Lion until he attempted to use Quintessence to save his wife Honerva which resulted in them both being corrupted by it, turning Zarkon into the heartless warlord he was known as. After a battle with the new Paladins of Voltron, he was gravely injured and his son Lotor took control of the empire, until he returned and retook command, naming his own son a traitor to the Empire and for him to be killed on sight. In a final battle, Zarkon fought his son, yet was overcome and finally killed by Lotor, his death splintering the Galra Empire.
Originating from the planet Daibazaal, Zarkon was originally a freedom fighter alongside King Alfor of Alteaand three others from different planets, despite their planets' histories of fighting one another. One night a comet fell from the sky while they were having dinner together. The people of Altea studied the unknown substance from the comet itself while the people of Daibazaal studied the crater it left since it seemed to lead to another world. After many years of experimenting, during which Zarkon married an Altean alchemist named Honerva, an unknown life form escaped from the rift. Worried this might doom their universe, Alfor presented five ships that he made from the comet, The Five Lions of Voltron, and Zarkon became the Black Paladin. Together they formed Voltron and destroyed the creature.
After the fight, Alfor suggested to close the rift to prevent more creatures coming through but Zarkon refused, fearing he'd lose the new power source it provided. This created a slight rift between the two.
Despite this they used Voltron along with the other Paladins to bring peace to the Galaxy over many years. However he and his wife grew obsessed with the power of Quintessence, as well as the possibility of it giving them immortality. Honerva grew ill during her studies and Zarkon tricked the other Paladins into going into the rift in an attempt to cure her, but they were both exposed to an overdose of the substance and the creatures they once fought.
And he is reprised by Neil Kaplan in the English dub and his Japanese voice is unknown, due to the loss of Kosei Tomita.