Mark Baum is a fictional character from the book and film adaptation titled "The Big Short," which explores the 2008 financial crisis. He is portrayed by actor Steve Carell and is based on the real-life hedge fund manager Steve Eisman. Mark is known for his sharp wit and critical perspective on the financial industry. In the story, Mark Baum leads a team that investigates the housing market's instability and the impending collapse of mortgage-backed securities. His character embodies the skepticism and moral outrage felt by some investors during the crisis, highlighting the ethical dilemmas within the financial system.