Desmond Pitt was in the army with Benjamin Grimm and after they mustered out they both became test pilots. After later re-enlisting, Pitt discovered several agents of Doctor Doom had infiltrated NASA. He decided to infiltrate them in turn.
When his wife died he got careless and was discovered and seemingly executed. Instead of killing Pitt, Doom turned him into the cyborg known as Darkoth, the Death Demon.
As he hadn't been able to confide in anybody, fearing Latverian spies everywhere, it seemed to the military that Pitt was a traitor.
After heroically sacrificing himself to save the life of the Thing, Pitt's soul was snatched by Mephisto before it reached its true destination. Mephisto, who was jealous of Thor's prior victory over him, called upon Darkoth (Pitt) to take the soul of Donald Blake (Thor's alter-ego) in return for his own soul. Pitt agreed, but only so he could return to his son, who was in an orphanage at the time. When Darkoth confronted a sleeping Blake he found himself unable to kill an innocent man and refused to do so. Mephisto intervened and forced Pitt to fight Thor for Blake's soul. Thor was victorious and even managed to free Darkoth from Mephisto's grasp by purging him of evil with his lighting and sending him to the afterlife. Afterwards, Donald Blake arranged for Pitt's son to be adopted by his new secretary and her husband.