Which Medici grand duke was Galileo's patron?

Cosimo II de' Medici was Galileo's patron. The Medici grand duke supported Galileo's career and helped give him a prestigious position at the Tuscan court.

Galileo had known Cosimo before he became grand duke: between 1605 and 1608, Galileo served as the young prince's tutor. After Cosimo succeeded his father in 1609, he appointed Galileo court mathematician and philosopher in 1610. The position freed Galileo from much of the routine teaching expected at a university.

Galileo reinforced the connection by dedicating Sidereus Nuncius to Cosimo and naming Jupiter's four newly observed moons the Medicean Stars. Cosimo II ruled Tuscany from 1609 until his death in 1621. The answer is sometimes confused with Cosimo I, who was the earlier Medici ruler and first grand duke of Tuscany, or Ferdinando II, Cosimo II's son and successor. Neither was Galileo's principal patron.