Capt. John Byron (7 February 1756 – 2 August 1791) was a British Army officer, best known as the father of poet Lord Byron.
Byron was the son of Vice-Admiral Hon. John Byron and Sophia Trevanion and grandson of William Byron, 4th Baron Byron of Rochdale. He was educated at Westminster School. He gained the rank of Captain in the Coldstream Guards. Captain John Byron also went by the nickname of "Mad Jack."
In 1778 he eloped with Amelia Osborne, Marchioness of Carmarthen, daughter of Robert Darcy, 4th Earl of Holderness, to Europe and they married after she obtained a divorce from Francis Osborne, 5th Duke of Leeds. They married on 1 June 1779 at London, England, and had a daughter, Augusta Maria Byron. Amelia Osborne died in 1784.
Byron then married Catherine Gordon, heiress of Gight in Aberdeenshire, Scotland, daughter of George Gordon and Catherine Innes, on 12 May 1785. She was the mother of George Gordon Byron, who would early in his life become the 6th Baron Byron. In order to claim his wife's estate in Scotland, Captain Byron took the surname Gordon. After he had squandered most of her fortune and deserted her, Mrs. Byron took her infant son to Aberdeen, Scotland, where they lived in lodgings on a meager income.
"Mad Jack" died in 1791 at age 35, at Valenciennes. Later, Lord Byron would tell friends that his father had cut his own throat. It is more likely he died from tuberculosis or an overdose.