The 1999 St. Louis Rams are the best underdog team story in NFL history.
The Rams were coming off a 4-12 season. They lost quarterback Trent Green to a knee injury in the preseason. They weren't expected to be any good. Instead, they won a Super Bowl.
Kurt Warner has become the poster boy for that underdog story, and for good reason. Warner's story has been told countless times: He went from bagging groceries to a regular-season and Super Bowl MVP. He ended up in the Pro Football Hall of Fame.