Miguel Humberto Díaz (born September 29, 1963) is an American theologian, diplomat and commentator who served as United States Ambassador to the Holy See. He was nominated by President Barack Obama and confirmed by the U.S. Senate on August 5, 2009. He resigned on November 5, 2012, and was immediately named University Professor of Faith and Culture at the University of Dayton. He was the first Hispanic U.S. Ambassador accredited to the Holy See.