Lieutenant-Colonel Sir Charles Richard Mackey O'Brien KCMG (13 December 1859 – 29 November 1935) was a British Army officer and colonial administrator. O'Brien was the youngest son of Sir Terence O'Brien, Governor of Heligoland and afterwards of Newfoundland. He was educated at Felsted School and the Royal Military College, Sandhurst, from which he was commissioned into the 30th Regiment of Foot (later the East Lancashire Regiment) in May 1878.