Frederick William II, Duke of Saxe-Altenburg

), was a duke of Saxe-Altenburg.

He was the youngest son of Frederick Wilhelm I, Duke of Saxe-Weimar and Anna Marie of Bavaria-Neuburg, his second wife. He born eight months after the death of his father, on 7 July 1602.

Shortly after his birth, Frederick Wilhelm II and his older brothers inherited Saxe-Altenburg as co-rulers under the guardianship of the Electors of Saxony Christian II and Johann Georg I until 1618, when his older brother Johann Philipp assumed the government of the duchy and the guardianship of his younger siblings.

By 1632, two of his three brothers were deceased. Frederick Wilhelm II and his older brother Johann Philipp began a dual government; but, in fact, Johann Philipp was the real and only ruler of the duchy of Saxe-Altenburg. Frederick Wilhelm II was only nominal ruler until the death of Johann Philipp (1639), when he began his personal reign over Altenburg.

In the Schloss Altenburg on 18 September 1638 Frederick Wilhelm II married firstly with Sofie Elisabeth of Brandenburg. She died in 1650 after twelve years of childless marriage.

In Dresden on 11 October 1652 Frederick Wilhelm II married secondly with Magdalene Sibylle of Saxony, Dowager Crown Princess of Denmark and daughter of his former regent, the Elector Johann Georg I. They had three children:
# Christian (b. Altenburg, 27 February 1654 - d. Altenburg, 5 June 1663). [http://www.royaltyguide.nl/images-families/wettin/saxonyernst2/1654%20Christian.jpg]
# Johanna Magdalene (b. Altenburg, 14 January 1656 - d. Weissenfels, 22 January 1686), married on 25 October 1671 to Johann Adolf I, Duke of Saxe-Weissenfels.
# Frederick Wilhelm III, Duke of Saxe-Altenburg (b. Altenburg, 12 July 1657 - d. Altenburg, 14 April 1672).

In 1660 he acquired the towns of Themar and Meiningen. In 1664 he built a hunting seat ("Jagdschloss") in Hummelshain, and, in 1665, he built a particularly beautiful widow seat ("Witwensitz") in Altenburg for his wife Magdalene Sybille, called "Magdalenenstift".

After his death he was succeeded by his second but only surviving son, Frederick Wilhelm III.