Clint Walker, a former merchant seaman and real-life deputy sheriff who roamed the West as a towering, solitary figure on “Cheyenne,” the first hourlong western on television, died on Monday in Grass Valley, Calif. He was 90. His death, at a hospital, was confirmed by his daughter, Valerie Walker, who said the cause was congestive heart failure. Mr. Walker lived in Grass Valley, about 60 miles northeast of Sacramento. Mr. Walker also appeared in the “The Dirty Dozen” and other movies, but he was best known for “Cheyenne,” seen on ABC from 1955 to 1963.