James Craig, 1st Viscount Craigavon PC PC (NI) DL, was a leading Irish unionist and a key architect of Northern Ireland as a devolved region within the United Kingdom. During the Home Rule Crisis of 1912–14, he defied the British government in preparing an armed resistance in Ulster to an all-Ireland parliament. He accepted partition as a final settlement, securing the opt out of six Ulster counties from the dominion statehood accorded Ireland under the terms of the 1921 Anglo-Irish Treaty. From then until his death in 1940, he led the Ulster Unionist Party and served Northern Ireland as its first Prime Minister. He publicly characterised his administration as a "Protestant" counterpart to the "Catholic state" nationalists had established in the south. Craig was created a baronet in 1918 and raised to the Peerage in 1927.

Unionism in Ireland is a political tradition that professes loyalty to the crown of the United Kingdom and to the union it represents with England, Scotland and Wales. The overwhelming sentiment of Ireland's Protestant minority, unionism mobilised in the decades following Catholic Emancipation in 1829 to oppose restoration of a separate Irish parliament. Since Partition in 1921, as Ulster unionism its goal has been to retain Northern Ireland as a devolved region within the United Kingdom and to resist the prospect of an all-Ireland republic. Within the framework of the 1998 Belfast Agreement, which concluded three decades of political violence, unionists have shared office with Irish nationalists in a reformed Northern Ireland Assembly. As of February 2024, they no longer do so as the larger faction: they serve in an executive with an Irish republican First Minister.