He spent 44 years in the Marine Corps. Mattis, a marine general, retired with four stars in 2013. Mattis has been known as 'Mad Dog' since leading troops in the Iraq War’s second Battle of Fallujah. He said some controversial things like: "It's fun to shoot some people." He was courted to run for President. There are reports that conservatives offered Mattis the chance to run as an independent in this year’s presidential election, but he declined. He easily changed Trump’s mind about waterboarding: After Trump met with Mattis on Tuesday, the President-elect told the New York Times that he changed his mind about the torture method. He’s really well-respected in Washington: While many of Trump’s cabinet picks have come under fire for their respectability, Mattis is incredibly well-respected in the military.