When Stark International finally abandoned the manufacture of weapons and arms technology, many of Tony Stark’s competitors were happy to take its place. None was so successful, however, as Hammer Industries, led by the unscrupulous and ruthless Justin Hammer, and it quickly became the world’s leading weapons supplier.

For years, Justin Hammer successfully maintained a front as a reclusive billionaire overseeing various international business interests, legal and otherwise. Hammer headed dozens of international design and manufacturing firms around the world, but, despite his many illegal activities, he avoided any trouble with the authorities by diversifying his interests.

Hammer and Tony Stark came into direct conflict when both competed to build an electronics plant in the small Communist country of Carnelia. To ensure his bid would be successful, Hammer had his engineers design a device to override the Iron Man armor (not knowing, of course that Iron Man was actually Tony Stark) and kill the Carnelian U.N. ambassador. Stark allowed his armor to be impounded as malfunctioning and tracked Hammer to the Mediterranean, where he discovered scores of Hammer’s dubious business practices, including the financing of superhuman criminals. With a spare Iron Man suit, Stark defeated Hammer’s agents and forced Hammer to escape. Although Iron Man was cleared of any murder charge, Tony Stark was never able to expose Hammer’s illegal activities. Later, seeking revenge, Hammer kidnapped Stark’s girlfriend Bethany Cabe aboard his submarine, but she was rescued by Iron Man and Hammer again escaped.

As with many of his superhuman agents, Hammer outfitted the criminal Force with technology and provided service for his high-tech battlesuit in exchange for one-half of all profits from his crimes. However, Clay Wilson, the inventor and operator of the Force armor, sickened of his criminal lifestyle and wanted out. Hammer seemed to support Clay in his decision, but actually slipped a device to kill Clay should he attempt to escape. Nevertheless, Force did escape, seeking out Tony Stark, who helped him destroy the fail-safe and escape from the army of supervillains Hammer sent after him. It was only Clay’s staged death that would prevent Hammer from bothering Clay ever again. Penalty indeed for any who might try to escape Hammer’s employ.

Over the years, Hammer supported, outfitted, and/or financed operations for many criminals, such as: Aqueduct, Blacklash, Beetle (Abe Jenkins) , Blizzard (Gregor Shapanka), Blizzard (Donald Gill), Blizzard (Randy Macklin), Blizzard (unidentified), Blue Streak, Boomerang, Cardinal, Captain Barracuda, the Constrictor, Cyclone (Unidentified), Discus, Eel (Edward Lavell), Eel (Leopold Stryke), El Toro Negro, Force, Leapfrog, Man-Killer, the Melter, Porcupine (Alexander Gentry), the Scorpion, Spymaster (spy), Spymaster (Number One), Stiletto, and Whiplash. Hammer's companies has also built weaponry for various villains, such as the Orb and the Viper II, and the Black Spectre and Zodiac criminal organizations.

At one point, Justin Hammer became involved in the "Great Game," a contest in which wealthy sponsors funded super-powered individuals so that they would battle each other, usually to the death. Hammer's avatar was El Toro Negro, who was often pitted against Spider-Man (Ben Reilly). When Spider-Man became involved directly, El Toro Negro went on a rampage that left most of the Great Game participants either dead or severely injured. Hammer shot El Toro Negro dead, and when it was discovered that rogue game players were assassinating CEOs of companies, Hammer and the other sponsors abandoned the game entirely.

Sometime later, Hammer needed a new saboteur to do industrial spying for him. Since the first one was very effective, Hammer decided to hire Taskmaster to train another Spymaster for him to replace the first one that was killed by the Ghost.

In recent months, Hammer learned he was dying, and he retired to a space station to spend the remainder of his days. He soon embarked on one last attempt on Tony Stark's life, hiring the villain Spymaster to inject Stark with nanite "rogue cells." The cells altered Stark's hormonal balance, making him incredibly irritable and dangerous. Stark's friend Jim Rhodes risked his life to save his friend, and, as Iron Man, Stark confronted Hammer at his space station. The battle ended when Hammer was injured as the space station exploded, freezing him in a block of ice, within which his body currently orbits the earth.