Doak Walker's friends said he fought the crippling ski injury that claimed his life as hard as he ever fought on the football fields that made him famous.

"Doak would not give up. He was tough until he died. His spirit, attitude, everything was incredible, very positive. He was a courageous individual," said friend John Nichols.Walker, the 1948 Heisman Trophy winner who starred on two NFL championship teams, was paralyzed in a skiing accident earlier this year. He died Sunday at age 71.

He was at Routt Hospital in his beloved Steamboat Springs, the ski resort 100 miles north of Denver where he had made his home for years.

The hospital said the cause of death was complications from the paralysis.

Walker was injured Jan. 30 when he hit a change of terrain, was tossed into the air and then slammed into the hillside. Nichols, who was with him that day, said he never saw Walker play football but had no doubt he was "a genuine hero. He was a man who didn't speak negatively about anybody or anything."

Staff at Craig Hospital in Englewood, where he began rehabilitation, marveled at his determination to recover.

Walker had regained some of his ability to talk through rehabilitation, during which he received thousands of letters and faxes from well-wishers and fans world-wide.

"His eyes would come alive, his expression was wonderful, he was able to talk in short phrases," said Rod Hanna, a family spokesman.

Shortly before he died, his wife Skeeter had gotten him a dog trained to help him get around.

The accident that robbed him of the use of his arms and legs was especially tragic for a Hall of Fame football player known for his breathtaking scoring runs. He is immortalized by the annual Doak Walker Award, which honors the nation's top college running back.