Machinehead is the technological resident genius from the Retaliators of Earth-8 and a pastiche of Marvel's Iron Man.
He uses his armor as weapon. His origins are unknown. Under his helmet, recently, Machinehead has exposed extended burned wound, the remains of a war fought in secret.
Machinehead first encounter with evidence of the multiverse was when Thunderer, the last hero from earth 7 attacked his analog from earth 8, Wundajin. In defense of Wundajin, Machinehead along with the rest of the Retaliators team, opposed to the recently arrived party of heroes. The conflict was alted when the attack of the Gentry erupted on earth 8 with the help of Lord Havok. Machinehead helped in the defense of his world but only with the help of heroes from every world, the Gentry was defeated, at least for the moment. Machinehead then accepted the invitation from President Superman to stay with the multiversal protectors in the house of heroes as part of Justice Incarnate
Machinehead appears to be one of the Justice League Incarnate member who seek out all Supermen in the multiverse. There was a threat eradicating all Supermen in the multiverse, therefore, they need to warn them before it's too late. They helped the Supermen from Multiple earths to defeat the being known as Prophecy but the team of Justice Incarnate lost his speedster, Red Racer.
When an attack of matter from the dark multiverse opened a breach between Earth 8 and Earth 23, Machinehead joined the Retaliators to thrust back the attack. Joining forces with the earth 8 Zen-Men, Machinehead and his allies mistook a lost Wally West with the cause of the menace. Wally deal with the confused heroes and dismantled Machinehead armor before neutralizing the real menace. Humbled, Machinehead and his teammates returned home, before the breach was closed.
In some moment under undisclosed circunstances, Earth 8 was invaded by another Earth. The heroes tried to fight the war in secret, but ultimately lost. Traumatize by his failure Machinehead started to question the idea of crossovers between worlds, something Justice Incarnate pushed for and started to work in secret against it, allying himself with Mr. Bones and Darkseid, to kept looking for ways to prevent crossover between universes. However, as they deal with Darkseid with the Psycho-Pirate as intermediary, it is unclear how much Psycho-Pirate influenced his thoughts and feelings.
Eventually Machinehead found a group of like minded individuals, The Injustice Incarnate. He secretly made a deal with Darkseid to help him achieve ultimate power in exchange for safety for his world. When the heroes started interfering with their plans, Machinehead wanted to continue fighting whiles Darkseid was disinterested and aparentelly, just executed Machinehead in the called Earth Omega. His body was left in a state of dimensional flux between Earth Omega and Earth 8. Doctor Multiverse tried to recover his remains but could only retrieve his helmet.
After the heroes of earth 8 confirmed the death of Machinehead, a new Machinehead joined the team. This new Machinehead (a evident reference to Marvel's War Machine) used shades of green in his armour and showeda more explicit armament, with several guns and cannons attached to the suit.