Justin Hammer in the movie Iron Man 2 was an incompetent and awkward rival who was mainly there to provide resources for the real villain, Whiplash. In the comics, Hammer was much, much more.
Ruthless and cunning, Justin Hammer was one of Tony Stark's greatest enemies, even though he had no powers or weapons of his own. Hammer was a billionaire industrialist who was driven more by the need for profit and power in the business world than any high ideals or desire for world domination. In his first appearance, Hammer was revealed as the man funding and providing technology for many of Iron Man's greatest enemies, like Whiplash and the Rhino. That gave Hammer an army of powerful super-villains at his command that he frequently launched en masse to attack both Iron Man and Tony Stark. Though Hammer was not a technological genius himself, he had some of the world's greatest scientists and engineers on his payroll. His labs could do almost anything, including seize control of Iron Man's armor, causing Stark to fire his repulsor and kill an ambassador. In short, Hammer was both Tony Stark's rival in business and crime.
I was disappointed that Iron Man 2 didn't make Hammer the powerhouse that he was in the comics. But I thought Sam Rockwell was hilarious.