Dhunam loved to hurt things. As a Grineer officer, he inflicted pain at any possible opportunity. So when he heard about Tyl Regor's experimental body augmentations, he clamored to become a subject. He didn't care about side effects, anything to become stronger.
The experiment left him sluggish and unresponsive. Weak of voice, he whispered for death. Instead, Regor ordered him beaten. The pain brought Dhurnam to life. He became a beast, eviscerating the unfortunate things sent to hurt him. Regor was pleased.
But the experiment was only a partial success. Without pain, Dhurnam grew weak again. Unfit for regular duty, the pits of Rathuum became his new home. The only place where he could find the steady diet of torment and suffering needed to survive.
Once a medical officer under Sargas Ruk, Thul failed to save the life of one of his favoured officers. Thul was "reassigned" to service under Kela as an Executioner of Rathuum. He has managed to survive under the protection of his allies, who value his medical skills.
The sole survivor of a frontier battalion that was eradicated by a lone Tenno, when Garesh eventually returned to civilization he was tried as a deserter and sentenced to death by Rathuum. To everyone's surprise he killed all his Executioners and was granted pardon on the condition that he himself become an Executioner. Garesh yearns for the day when he can punish a Tenno.
Gorth was a distinguished member of the Nightwatch Corps, but when he unwittingly killed a close ally of Lech Kril for stealing supplies he faced political fallout that destroyed his career. Exiled from military service, Gorth now seeks to redeem his honor as an Executioner of Rathuum.
Olka Harkonar hails from the Harkonar Production Zone. She is one of the few nobles not satisfied by simply watching her weapons wreak havoc, she needed to join the fray. So Olka Harkonar became an Executioner of Rathuum, vowing to prove the might of Harkonar weapons and armor with every judgement she made.
Nok led a decorated career in service to Captain Vor, tasked with routing out any weak or anarchic influences within the ranks of the Grineer army. After many years of loyal service, the degenerative effects that plague all Grineer began taking their toll on Nok. With Vor's blessing, Nok was granted leave to spend his remaining days punishing Grineer in the court of Rathuum.
Reth was once a simple labourer working in the shipyards of Ceres. He often wondered how lethal the equipment he worked with could be if he made only minor tweaks to its design. After a series of escalated killings his handiwork was discovered by his superiors. Rather than risk being captured, Reth fled to Kela, where he now tests his latest machinations in the service of Rathuum.
Not much is known about the mysterious Zura. She appeared in the fighting pits with her Hyekka and carved a bloody path through the opposition. The crowd always roars with pleasure when Zura steps into the fighting pits.