Sean O'Callaghan (10 October 1954 – 23 August 2017) was a member of the Provisional Irish Republican Army (IRA), who from the late 1970s to the mid-1980s worked against the organisation from within as an intelligence agent for the Irish Government with the Garda Síochána's Special Branch. In the mid-1980s he left the IRA and subsequently voluntarily surrendered to British prosecution for actions he had engaged in as an IRA gunman in the 1970s. Following his release from imprisonment, he published a memoir detailing his life in Irish Republican paramilitarism entitled The Informer: The True Life Story of One Man's War on Terrorism (1998). Former Irish Prime Minister Garret FitzGerald described O'Callaghan as one of the Irish Government's most important spies operating within the Provisional IRA during the late 20th century's The Troubles. Early life O'Callaghan was born on 26 January 1954, into a family with a Fenian paramilitary history, in Tralee, County Kerry. His paternal grandfather had taken the Anti-Treaty side during the Irish Civil War, and his father had been interned by the Irish Government at the Curragh Camp in County Kildare for IRA activity during World War II. By the late 1960s, the teenaged O'Callaghan had ceased practising the Catholic faith, adopted atheism and had become interested in the theories of Marxist revolutionary politics, which found an outlet of practical expression in the sectarian social unrest in Northern Ireland at that time, centred on the activities of the Northern Ireland Civil Rights Association. In 1969, an outbreak of communal violence broke out in Northern Ireland and believing that British imperialism was responsible, O'Callaghan joined the newly founded Provisional IRA at the age of 17. Soon afterwards, he was arrested by local Gardaí after he accidentally detonated a small amount of explosives, which caused damage to the homes of his parents and their neighbours. After demanding, and receiving, treatment as a political prisoner, O'Callaghan quietly served his sentence. Provisional Irish Republican Army activity After becoming a full-time paramilitary with the IRA, in the early to mid 1970s O'Callaghan took part in over seventy operations associated with Irish Republican political violence including bomb materials manufacture, attacks on IRA targets in Northern Ireland, and robberies to provide funding for the organisation. On 2 May 1974 he was part of an attack by an IRA force on a 6th Battalion, Ulster Defence Regiment (UDR) base at the village of Clogher in