Kettler was born near
Anröchte,
Kreis Soest, of an old
Westphalian noble family and the ninth child of the German knight Gotthard Kettler zu Melrich (mentioned 1527–1556) and his wife Sophie of
Nesselrode. Gotthard's older brother Wilhelm Kettler was the
bishop of Münster from 1553 to 1557. Kettler enlisted in the
Livonian Order around 1537 and became a knight. In 1554, Gotthard Kettler became
Komtur of
Dünaburg (Daugavpils), and in 1557,
Komtur of
Fellin (Viljandi). In 1559, during the
Livonian War (1558–1582), he succeeded
Wilhelm von Fürstenberg as Master of the
Teutonic Order in
Livonia. When the
Livonian Confederation came under increasing pressure from
Ivan IV of Russia, Kettler converted to
Lutheranism and secularised
Semigallia and
Courland. On the basis of the
Treaty of Vilnius (28 November 1561), he created the
Duchy of Courland and Semigallia as a
vassal state of the
Grand Duchy of Lithuania, which was soon merged into the
Polish–Lithuanian Commonwealth. Following the duke's proposal in 1567, the regional assembly (
landtag) decided to build 70 new churches and 8 schools in the remote areas of the duchy where many peasants still lived and died unbaptized. He died on 17 May 1587 in
Mitau (Jelgava), aged 70. His heirs ruled in Courland until 1737. == Family ==