Joachim Cornelis Theodorus Frederik Jacobus Mackay, Hertog van Baronië, Landgraaf van Germania en Erfgroothertog van Nova Batavia is a Batavian politician and former Prime Minister. He was one of the main architects of the shortlived Batavian re-unification and an important figure in the movement to preserve the Batavian culture under Jingdaoese occupation. He served as Prime Minister of Batavia for two terms, one under Jingdaoese occupation, and one during the re-unified Kingdom. Personal conflict with his successor, Gustaaf Vermeylen, lead him to abandon public life and take on a job as librarian at the University of Davignon.
During the Shirithian annexation of Dietsland, Mackay returned to the forefront of political life, and became the leader of the Free Batavians, a resistance movement that fought for the reinstitution of the Batavian Kingdom and self-determination for the ethnic Batavian people.