Justin Hammer is a fictional character that has appeared in various comic book series published by Marvel Comics. As a frequent adversary of the superhero Iron Man, Justin Hammer exists in Marvel's main shared universe, known as the Marvel Universe.
Justin Hammer was born in Surrey, England, and later became a citizen of Monaco. A rival of industrialist Anthony Stark (Iron Man), multi-billionaire businessman Hammer, himself an industrialist, later became a criminal financier. Hammer uses unethical methods. In exchange for fifty percent of the profits from their crimes, he will pay bail for costumed criminals and finance the development and replacement of their weaponry and equipment.
Hammer invented a device called the hypersonic scan transmitter, which allowed him to take control of Iron Man's armor. He tested this remote control, affecting Iron Man's unibeam, sealing plates, and boot jets. Angered that he had lost a lucrative bid to Stark International, Hammer took control of Iron Man's armor and forced him to kill the Carnelian ambassador, and set an army of superhuman criminals against Iron Man. Stark cleared his name and destroyed the control device, but had found a new enemy in Hammer.
It was revealed, years later, that Justin Hammer had obtained Stane International after the death of its chairman Obadiah Stane, causing problems for Tony Stark through his old company. With operatives of HYDRA, Roxxon Oil, Moroboshi International, and the Trinational Commission, Hammer tricked the Masters of Silence into attacking Stark Enterprises. Even when Hammer was forced to sell his stock in Stane International to Stark for the sum of one dollar, Hammer had the last laugh, when all the shady dealings and irresponsible, or even criminal actions of Stane International came back to bite Tony later.
Much later, after Justin Hammer had been diagnosed with an incurable illness, he resolved to destroy Tony Stark before he died. Hammer infected Stark's bloodstream with mood-altering nanites that made Stark irrational and temperamental. In a final confrontation between Iron Man and Hammer on Hammer's own space station, Hammer was accidentally frozen in a block of ice and lost in space. Hammer Industries kept running, long enough for employees to forget exactly what happened to Justin.