Justin Hammer is a fictional character in the Marvel Comics universe, primarily known as a villain and rival to Tony Stark, also known as Iron Man. He is portrayed as a wealthy industrialist and arms dealer who seeks to outdo Stark in technology and business. Hammer often employs advanced weaponry and technology to challenge Iron Man. In the Marvel Cinematic Universe, Justin Hammer is played by actor Sam Rockwell and appears in the film Iron Man 2. In this movie, he attempts to create his own line of armored suits to compete with Stark Industries, showcasing his ambition and desire for power in the high-stakes world of technology and defense.