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| Friedrich Casimir Kettler | |
|---|---|
 Portrait by an unknown Swedish painter, 18th century | |
| Duke of Courland and Semigallia | |
| Reign | 1 January 1682– 22 January 1698 |
| Predecessor | Jacob Kettler |
| Successor | Frederick Wilhelm Kettler |
| Born | 6 July 1650 Mitau |
| Died | 22 January 1698 (aged 47) Mitau |
| Burial | Ducal crypt in Schloss Mitau. |
| Spouse | Sophie Amalie of Nassau-Siegen Elisabeth Sophie of Brandenburg |
| Issue | Frederick Wilhelm Kettler |
| House | House of Kettler |
| Father | Jacob Kettler |
| Mother | Louise Charlotte of Brandenburg |
| Religion | Lutheranism |
Frederick Casimir Kettler (German: Friedrich Casimir Kettler; 6 July 1650 – 22 January 1698) was Duke of Courland and Semigallia from 1682 to 1698. Frederick Casimir was the son of Jacob Kettler and Louise Charlotte of Brandenburg. In his reign the Duchy lost its geopolitical position and became Sweden, Prussia and Russia's territorial subject of interests.