FRANCIS I. (1708-1765), Roman emperor and grand duke of Tuscany, second son of Leopold Joseph, duke of Lorraine, was born on Dec. 8, 1708. He married in 1736 Maria Theresa (q.v.), daughter of the emperor Charles VI. He succeeded his father as duke of Lorraine in 1729, but the emperor, at the end of the Polish War of Succession, desiring to compensate Stanislaus Leszczynski for the loss of his crown in 1735, persuaded Francis to exchange Lorraine for the reversion of the grand duchy of Tuscany. His wife secured his election to the Empire on Sept. 13, in succession to Charles VII., and she made him co-regent of her hereditary dominions. Francis was well content to leave the reality of power to his able wife. He died at Innsbruck on Aug. 18, 1765. See MARIA THERESA.