Whether he is the best running back in NFL history is debatable. Whether he's the most productive isn't. Smith holds league records for rushing yards (18,355) and touchdowns (164).
Dirk turned from Dallas hero to legend when he led the Mavericks to their first championship last season. Before that, Nowitzki had been heralded as one of the best shooting big men in NBA history and an 11-time NBA All-Star.