Dunn was born in York, Upper Canada (later Toronto, Ontario) in 1833, the son of John Henry Dunn, Receiver General of Upper Canada, and studied at Upper Canada College.Upper Canada College: Alexander Roberts Dunn 1848. When his family returned to England, he attended Harrow School. In 1852 at the age of 19, he purchased a commission in a cavalry regiment in the British Army, the 11th Hussars (Prince Albert’s Own). Dunn was six feet, three inches tall, and commissioned a special four foot long sabre from Wilkinson Sword to accommodate his height.Arthur Bishop, "Canada And The Victoria Cross: Part 1 of 18", Legion — Canada's Military History Magazine, January 1, 2004.
