He's a documentary filmmaker who made a name for himself with a film called "Roger & Me", which is about Detroit's rise and fall in the US auto industry. He's from Detroit, and chose a subject that affected his life as his debut. He also defied documentary filmaking rules by choosing to be in front of the camera the whole time.
He later made Bowling for Columbine, which was about the school shooting in CO as well as America's fascination with guns. It got a major theatrical release and made a pretty big name for itself.