Supreme Leader Abelt Dessler, ruler of the Garmillas Empire, spearheaded a brutal galactic expansion driven by his home planet's environmental collapse. Confronted with Garmillas' destruction from volcanic activity and atmospheric poisoning, he targeted Earth as a new home, deploying radioactive planet bombs to sterilize it. His strategies proved methodical and ruthless, leveraging advanced technology and calculated aggression. Beneath his authoritarian rule lay deep, unrequited affection for Queen Starsha of Iscandar, whose pacifist ideals clashed with his expansionism. This connection occasionally surfaced, revealing complexity beneath his hardened exterior.

After the Yamato thwarted his plans by obtaining Iscandar's radiation-cleaning device, Dessler confronted the ship at Garmillas. His Dessler Cannon attack failed when the beam reflected back, seemingly killing him. He activated an emergency teleport moments before impact, surviving critically injured and adrift in space. Recovered by the White Comet Empire, its leader Emperor Zwordar integrated Dessler into their forces despite objections. Dessler accepted a fleet and flagship, initially aligning with the empire to pursue his vendetta against the Yamato.

Serving under Zwordar, Dessler devised intricate traps: deploying space bacteria disguised as fireflies to cripple the Yamato and luring it into an electromagnetic sensor-laden asteroid for a cannon strike. These schemes consistently failed due to the Yamato's resilience and external interference, including sabotage by Zwordar's advisor Sabera. When Sabera falsely accused Dessler of treason, Zwordar imprisoned him. Dessler escaped with his loyal aide Talan, taking Sabera hostage. Sabera attempted to execute him during their flight, but Zwordar intervened upon realizing her deception, restoring Dessler's command.

Dessler's pivotal shift occurred during a final confrontation with the Yamato near Earth. After deploying warp-capable mines to prevent the ship from firing its Wave-Motion Gun, he engaged in a direct showdown. Facing Susumu Kodai at gunpoint aboard his flagship, he prepared to kill him until Kodai collapsed from exhaustion. Witnessing Yuki Mori's immediate, selfless care for Kodai stirred a profound realization in Dessler about love and loyalty. He relinquished his weapon, handed Kodai's pistol to Yuki, and revealed critical intelligence on destroying the Comet Empire's capital, Gatlantis. He then ordered his fleet to withdraw, ending his conflict with Earth.

Later, Dessler led the remnants of the Garmillas fleet seeking a new homeworld. Returning to the Garmillas system for a final farewell, he discovered alien invaders desecrating the planet. Enraged, he ambushed their mining operation, inadvertently triggering a chain reaction that destroyed Garmillas completely. Escaping with his fleet, he pursued the displaced planet Iscandar to warn Starsha and her consort Mamoru Kodai of approaching threats, demonstrating his continued protective concern for Starsha despite her rejection. This act solidified his transition from conqueror to reluctant ally of former enemies.