Lucius O'Brien, 15th Baron Inchiquin

Lucius William O'Brien, 15th Baron Inchiquin (21 June 1864 – 9 December 1929) was the England-born holder of a hereditary peerage in the Peerage of Ireland, as well as Chief of the Name of O'Brien and Prince of Thomond in the Gaelic Irish nobility.

O'Brien was born in England the second of four children, and oldest son, to Edward O'Brien, 14th Baron Inchiquin and first wife Emily A'Court, at Belmore near Bishop's Waltham, Hampshire. He was educated at Eton College.

O'Brien was commissioned into the Royal Irish Rifles in 1885, transferring in 1886 to the English Rifle Brigade regiment in which he served until 1893. He was later Honorary Colonel of the Clare Royal Field Artillery Reserve Volunteers.

Politically a Conservative, O'Brien unsuccessfully stood for the British House of Commons by contesting the Eastern Division of County Clare in 1885. He was State Steward to the Lord Lieutenant of Ireland in 1895. He succeeded his father's peerage in 1900, serving hence as an Irish Representative Peer in the House of Lords. In 1921 he was appointed to the Senate of Southern Ireland which was abolished next year by the formation of the Irish Free State.