Tony Dungy wasn't the first African-American to become a head coach in the NFL (Art Shell, Raiders) and he may not end up as the best one (that title could go to Mike Tomlin, a former assistant to Dungy), but he has changed the game in two important ways.
First, Dungy is the first black head coach of a Super Bowl champion -- the Indianapolis Colts, who won Super Bowl XLI. That Super Bowl guaranteed a champion with a black head coach because Bears' coach Lovie Smith is also African-American.
Second, Dungy proved that African-American coaches who have dignity, intellectualism, integrity and respectability are viable coaching candidates. Dungy's not a nail-chewing firebrand like Mike Singletary or a butt-kicker like Shell (in his first stint at Oakland, not his second). That's the mold owners sought for African-American coaching candidates. He's more like Bill Walsh than Bill Parcells.
And he won: 148 times overall, a Super Bowl, an armful of division titles and 11 playoff berths in 13 years on the job. There are better coaches in the game, but that list is VERY short. There are few who have or will come close to Dungy in terms of respect and class.
His yellow blazer for the Pro Football Hall of Fame should be in production soon.