Roland Hamilton was the son of a New York City banker. He was born into wealth and grew up to become a playboy and gambler. He was drafted into the army in World War II. He continued to gamble in private games. He got into a fight in one such game and killed an opponent. He was arrested for manslaughter and ended in the Deadly Dozen. He received rigorous training from Dum-Dum Dugan.
Under Dugan, Hamilton acted as the laziest member of the Dozen. His card skills proved useful in their initial mission.
By the time Kelly took over the unit, Hamilton had become an expert in combat with knives, machine guns and grenades. But at the cost of his sanity. He started displaying sadistic and psychotic behavior. He started killing people "for the fun of it". Enemy combatants and prisoners of war were all fair game for him. In the last mission of the Dozen, Hamilton started killing all enemy personnel available. Including defenseless nurses. His murder spree was only stopped by the bullet of one of the German guards.