The Manhunter Highmaster is the overseer of the Manhunters' birthing process and creations. When Doctor Fate and other heroes made it to the Manhunter planet and fought their way to the birthing chambers the Highmaster continued to create Manhunters even as the heroes began to destroy them. Realizing that his efforts were futile the Highmaster relocated off the Manhunter's planet in search of the Guardians to destroy.
He tracked the Guardians to their hidden realm and it took the combined might of the life forces of several super heroes possessed in Superman and Green Lantern (Hal Jordan) to track him through the ether. The Highmaster laid traps and false endings to try and dissuade the heroes.
In the secret dimension the Highmaster locked Superman in a high intensity gravity inducer and used a time accelerator to suck the energy out of Green Lantern's ring requiring Hal Jordan to call upon the Guardians as living Oan power batteries. With their combined might they could have easily defeated the Highmaster.
However, the Manhunter Highmaster forced Hal Jordan to call on the Guardians to charge his battery and help him; thus exposing the Guardians to the Highmaster's attacks. The Highmaster was ready to destroy the Oans but for the interference of Superman. The Man of Steel battered the Manhunter as the emerald warrior was supercharged by the Guardians' energy.
During the fight, Superman had been blasting the Highmaster with his heat vision. The Manhunter was glowing red hot, Jordan was able to destroy the once-yellow Highmaster. After its destruction, the Manhunters would go into suicidal overdrive. There would be no way the Guardians could stop them.