Friedrich Kettler
Friedrich Kettler August 1642 was Duke of Courland from 1587 to 1642.
Friedrich Kettler was born to Gotthard Kettler and his wife Anna of Mecklenburg. The first of two sons, Friedrich in his youth had a good education travelled to many other European countries. According to Gotthard Kettlers will, the Duchy was to be divided between his two sons. After his fathers death in 1587, Friedrich and his younger brother Wilhelm became corulers of the Duchy. After Wilhelm reached majority in 1596, the Duchy was officially partitioned into its Courland and Semigallian parts.
Source: Wikipedia