Commander Yurak was commander of the Doom Forces.
Voltron: Defender of the Universe Continuity
In both versions, he is disgraced for his losses to Voltron. He is transformed into a gigantic Robeast in hopes of redeeming himself. However, he is killed by GoLion/Voltron. Yurak's death is one of the few onscreen character deaths that were retained for the American Voltron release.
An Old commander, Yurak obviously survived his fair share as shown by his cybernetic eye and arm. As a Robeast, he mostly retained his old appearance except with longer ears and an additional robotic arm. Robeast Yurak also kept his personality and intelligence unlike Avok and Twyla's brother.
Yurak had presumably been in the Doom military for decades by the time of the massive bombing of Arus.  In the aftermath of the return of Voltron, he led several raids against Arus, often assisted by the witch Haggar and her robeasts.
After failing to destroy Voltron and conquer Arus, Yurak begged for mercy from Zarkon and the nobles of Doom, but the king banishes him. Just then, Lotor intervenes, offering Yurak one last chance. Yurak would become a robeast, and take down the lions while Lotor had Keith distracted. Yurak was able to take down four lions, but Keith returned in Black Lion, Voltron was combined, and Yurak was slain. 
With Yurak's demotion and later death, Zarkon appoints Lotor as commander of the Doom Forces.
Yurak also appears in the Voltron video game for mobile phones. Robeast Yurak is an unlockable playable fighter in arena mode.