Wilhelm Kettler (20 June 1574 – 7 April 1640) was the Duke of Courland, a Baltic German region in today's Latvia.

[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.

His son, Jacob Kettler, succeeded Friedrich as Duke of Courland and Semigallia in 1642.

[3] Wilhelm's remains were returned to Courland in 1642, and he was interred in the ducal tomb on 23 February 1643.