He's led his team to more victories than any other coach in N.F.L. history. But on January 4, after 26 years with the Miami Dolphins, football coach Don Shula announced he is retiring. "It was a tough decision," he said. Shula's team went to six Super Bowls, and their 17-0 season in 1972 was the best ever in the N.F.L. Former Dallas coach Jimmy Johnson, whose Cowboys won two Super Bowls, will replace Shula.