Born about 1868 or 1869, Amos was the son of Bad Heart Bull ("Tȟatȟáŋka Čhaŋtéšiča") and his wife Red Blanket ("Tȟašína Lúta Wiŋ"). Amos' father was a brother of the headman He Dog and a nephew of the famous Oglala chief Red Cloud. Known as Eagle Bonnet ("Waŋblí Wapȟáha") as a young man, Amos grew up living the traditional life of the Oglala Lakota. His family belonged to an Oglala camp known as the Soreback Band. He was eight years old when George Armstrong Custer's column attacked the large Indian village in the Battle of the Little Bighorn in 1875. The Sioux decisively defeated Custer's forces.