He was the adjutant for George Armstrong Custer and was killed during the Battle of the Little Bighorn.

[1] At the age of 14, he moved to Buffalo, New York to continue his studies.

He rose to first lieutenant on December 14, 1864, but did not return to front-line duty until March 1865.

He was awarded brevet promotions to captain, major, and lieutenant colonel for his meritorious service during the war, the last of his actions occurred at the Battle of Sayler's Creek during the Appomattox Campaign.

After the war, he immediately joined the 1st New York Provisional Cavalry and applied for a Regular Army commission.

[1] The Grand Army of the Republic in Hamilton is named in Cooke's memory and honor.