Terence Marne O'Neill, later created Baron O'Neill of the Maine, PC (10 September 1914 – 12 June 1990) was the fourth Prime Minister of Northern Ireland and leader (1963–1970) of the Ulster Unionist Party (UUP). A moderate who sought to reconcile the sectarian divisions in Northern Ireland society, he was Member of the Parliament of Northern Ireland for the Bannside constituency from 1946 until his forced resignation in 1970 as communal conflict erupted; his successor in Parliament was Ian Paisley, while control of the UUP passed to harder-line elements.
Terence O'Neill was born on the 10 September 1914 at 29 Ennismore Gardens, Hyde Park, London. He was the youngest son of Lady Annabel Hungerford Crewe-Milnes (daughter of the Marquess of Crewe) and Captain Arthur O'Neill of Shane's Castle, Randalstown, the first MP to be killed as a result of World War I. The family assumed the surname O'Neill by royal license in lieu of their original name Chichester. The Chichesters trace their lineage to the name O'Neill through Mary Chichester, daughter of Henry O'Neill of Shane's Castle.
Terence O'Neill grew up in London and was educated at West Downs School, Winchester and Eton College. He spent summer holidays in Ulster. Following school he spent a year in France and Germany and then worked in the City of London and Australia. In May 1940 he received a commission at the Royal Military Academy Sandhurst and went on to serve in the Irish Guards during WWII, in which both his brothers died. Like many Unionist politicians, the rank he held during the war would follow him in his political career, hence "Captain" Terence O'Neill. Although coming from a long line of Protestants he attempted to reconcile the Catholics and the Protestants of Northern Ireland. It was discovered recently that after his plane was shot down on a mission over the Netherlands he was sheltered by a Catholic family together with other wounded soldiers and Jewish refugees. His experiences in hiding with this family led him to visit them frequently once the war was over and to make attempts to create harmony between Protestant and Catholic communities.
On 4 February 1944 he married Katharine Jean (16 January 1915 - 15 July 2008), the daughter of William Ingham Whitaker, of Pylewell Park, Lymington, Hampshire. They had one son, Patrick (b. 1945), and one daughter, Anne (b. 1947).