the third son of Grand Duke Cosimo II de' Medici of Tuscany and Archduchess Maria Maddalena of Austria. He was governor of Siena, with interruptions, from 1629. He never married. career at the age of 16. His father, Cosimo II, died on 28 February 1621; he was succeeded by Ferdinando de' Medici, the elder son. On 29 May 1629, Grand Duke Ferdinando appointed Mattias governor of Siena, following the death of their aunt and the then governor, Catherine de' Medici.
