| Wilhelm Kettler | |
| Duke of Courland and Semigallia | |
| Succession: | Duke of Courland |
| Reign: | 1587–1617 |
| Predecessor: | Gotthard Kettler |
| Successor: | Friedrich Kettler |
| Issue: | Jacob, Duke of Courland |
| House: | Kettler |
| Father: | Gotthard Kettler |
| Mother: | Anna of Mecklenburg |
| Birth Date: | 20 June 1574 |
| Birth Place: | Mitau, Duchy of Courland and Semigallia |
| Death Place: | Kucklow, Duchy of Pomerania |
| Burial Place: | Ducal crypt in the Jelgava Palace |
| Religion: | Lutheranism |
Wilhelm Kettler (20 June 1574 - 7 April 1640) was the Duke of Courland, a Baltic German region in today's Latvia. Wilhelm ruled the western Courland portion of the Duchy of Courland and Semigallia, while his brother Friedrich ruled the eastern Semigallia portion.
Born in Mitau in 1574, Wilhelm Kettler was the youngest son of Gotthard Kettler and his wife, Anna of Mecklenburg. After their father's death in 1587, Friedrich inherited the title of Duke of Courland and Semigallia, but economic control was split between Wilhelm and Friedrich.[1] The brothers divided the duchy between themselves, and Wilhelm ruled the Courland portion, with the seat in Kuldīga.[2]
In 1609, William married Princess Sophia of Brandenburg-Prussia (1582–1610), daughter of Albert Frederick, Duke of Prussia, receiving as a dowry the territory of Grobiņa.
Due to conflicts with the local nobility, he lost control of the duchy in 1617 and emigrated.[3] Thereafter, his brother Friedrich became the sole ruler of the duchy.
He died in the Kucklow abbey in Pomerania on 7 April 1640. His son, Jacob Kettler, succeeded Friedrich as Duke of Courland and Semigallia in 1642.
Wilhelm's remains were returned to Courland in 1642, and he was interred in the ducal tomb on 23 February 1643.