Cook was born on the Pamunkey Reservation in King William County on October 23, 1860. His father, Major Cook, died in 1861, and his mother, Caroline Bradby Cook, raised him with the help of her father and brother. Members of the Colosse Baptist Church before the American Civil War (1861–1865), the Bradby and Cook families numbered among the many Pamunkey who formed Pamunkey Indian Baptist Church after the war. Cook’s mother brought him up as a member of the church, and, like most Pamunkey, the Cooks remained a devoutly religious family. In 1901 he was the first delegate from the church to the Baptist General Association of Virginia.