Maurice, Duke and Elector of Saxony (1521-53) was a German prince best known for betraying the Protestant cause in the 1540s before turning on Charles V at the start of the 1550s and forming an alliance with the French.
In 1485 Saxony had been split between the brothers Ernest and Albert. Ernest got the title of elector and Thuringia, Albert got the title of duke and the area ruled from Leipzig.
Maurice was the son of Henry, duke of Albertine Saxony. He converted to Protestantism in 1539, and inherited his father's lands two years later, in 1541.
During the 1540s Maurice refused to take up arms in support of the Lutheran cause. He had been a member of the League of Schmalkalde, but left in 1542. He fought in Charles's army during the invasion of France of 1544, the campaign that stalled outside Saint-Dizier (19 June-18 August 1544) during the Fourth Hapsburg-Valois War of 1542-44.
At the Diet of Regensburg of 1546 he was offered the title and lands of the equally Protestant John Frederick, Elector of Saxony in return for his neutrality. He accepted the offer and this helped Charles V win a victory over the Protestants at Mühlberg (1547). This didn't look to be the case at first. The dispossessed Elector John Frederick used his army to reoccupy his part of Saxony and overrun Maurice's part. This forced Charles to take the field in person, leading to the victory at Muhlberg. John Frederick was captured at this battle and kept in captivity. After the battle John Frederick was forced to agree to Maurice's occupation of the Electorate.
Maurice now found himself in a difficult position. He was still a Protestant, and supported the Lutheran faith in his lands, but he was seen as a traitor by many of his fellow Protestants. He refused to issue Charles's 'Interim', an attempt to solve the religious divide, and instead issued a modified 'Leipzig Interim' in 1549.
In 1551 Maurice and a number of other German Protestant princes formed an alliance with Henry II of France. This was formally sealed at Chambord on 15 January 1552, and was a key event in the course of the fifth and final Hapsburg-Valois War. The Princes agreed to give Henry the three bishoprics of Toul, Metz and Verdun, in western Lorraine, in return for his support. Henry occupied the bishoprics in March 1552, catching Charles somewhat out of place. He attempted to reach the Netherlands to join a loyal army, but instead found his route blocked by Maurice and the Protestant forces (Maurice only just failed to capture Charles and Innsbruck). Eventually Charles was forced to agree to the Peace of Passau of 1552, in which he temporarily came to terms with his Protestant subjects. This allowed him to mount the unsuccessful siege of Metz (October 1552-January 1553). At the same time Maurice joined Charles's brother Ferdinand, who was campaigning in Hungary, although he returned home before the siege had been lifted.
Maurice was brought down by a disagreement with Albert II 'Alcibiades', margrave of Brandenburg. Albert was a Protestant, but he had been a supporter of Charles V during the 1540s. In 1550 he sided with Maurice, but fell out with him in April 1552, after the formal alliance with France. Charles V welcomed Albert back into his service, but this triggered an alliance of Catholic and Protestant princes hostile to him. The allies attacked Albert and defeated him at the battle of Sieverhausen (9 July 1553), but Maurice was mortally wounded in the battle, dying on 11 July. Albert was defeated again in September and forced into exile.
In 1554 most the Ernestine line regained most of its lost lands, but Maurice's descendents in the Albertine line retained the electorate until 1806.