CHICAGO — Hall of Famer Gale Sayers, who made his mark as one of the NFL’s best all-purpose running backs and was later celebrated for his enduring friendship with a Chicago Bears teammate with cancer, has died. He was 77. Nicknamed “The Kansas Comet” and considered among the best open-field runners the game has ever seen, Sayers died Wednesday, according to the Pro Football Hall of Fame. Relatives of Sayers had said he was diagnosed with dementia.