text: Seamus Costello (, 1939 – 5 October 1977) was an Irish politician. He was a leader of Official Sinn Féin and the Official Irish Republican Army and latterly of the Irish Republican Socialist Party (IRSP) and the Irish National Liberation Army (INLA).
  He argued for a combination of socialist politics on economic issues and traditional physical force Irish republicanism. He is best remembered for the founding of the IRSP and the INLA. He was a victim of a feud with his former comrades in the Official IRA.
  Early life and IRA Border Campaign
  Born into a middle-class family in Bray, County Wicklow, he was educated at Christian Brothers College, Monkstown Park. He left school at 15 and became a mechanic and later car salesman in Dublin.
  At the age of 16 he joined Sinn Féin and the Irish Republican Army. Within a year, he was commanding an active service unit in south County Londonderry during the Border Campaign, where his leadership skills and burning down of the courthouse in Magherafelt earned him the nickname of "the Boy General". The unit's most publicised actions included the destruction of bridges.