Arlene Isobel Foster, Baroness Foster of Aghadrumsee,, is a British broadcaster and politician from Northern Ireland who served as First Minister of Northern Ireland from 2016 to 2017 and 2020 to 2021 and leader of the Democratic Unionist Party (DUP) from 2015 to 2021. Foster was the first woman to hold either position. She is a Member of the House of Lords, having previously been a Member of the Legislative Assembly (MLA) for Fermanagh and South Tyrone from 2003 to 2021.

The First Minister and deputy First Minister of Northern Ireland are the joint heads of government of Northern Ireland, leading the Northern Ireland Executive and with overall responsibility for the running of the Executive Office. Despite the titles of the two offices, the two positions have the same governmental power, resulting in a duumvirate; the deputy First Minister, customarily spelled with a lowercase d, is not subordinate to the First Minister. Created under the terms of the 1998 Good Friday Agreement, both were initially nominated and appointed by members of the Northern Ireland Assembly on a joint ticket by a cross-community vote, under consociational principles. That process was changed following the 2006 St Andrews Agreement, such that the First Minister now is nominated by the largest party overall, and the deputy First Minister is nominated by the largest party from the next largest community block.