Mark Steven Kirk is an American politician and attorney who served as a United States Senator from Illinois from 2010 to 2017. A member of the Republican Party, he previously served five terms in the U.S. House of Representatives for Illinois's 10th congressional district. Before his political career, Kirk served for 23 years in the U.S. Navy Reserve as an intelligence officer, retiring with the rank of Commander. Known as a moderate Republican, he often focused on fiscal conservatism and national security while holding socially moderate views.