|Duke of Courland and Semigallia|
|Born||February 2, 1517|
Anröchte, Kreis Soest, Duchy of Cleves
|Died||May 17, 1587 (aged 70)|
Mitau, Duchy of Courland and Semigallia
|Burial||Ducal crypt in the Jelgava Palace|
|Spouse||Anna, Duchess of Mecklenburg|
|Father||Gotthard Kettler zu Melrich|
|Mother||Sophie of Nesselrode|
Gotthard von Kettler (also Ketteler, German: Gotthard Kettler, Herzog von Kurland; 2 February 1517 – 17 May 1587) was the last Master of the Livonian Order and the first Duke of Courland and Semigallia.
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 bishop of Münster from 1553 to 1557.
In 1554 Gotthard Kettler became Komtur of Dünaburg, and in 1557 Komtur of Fellin. In 1559, during the Livonian War (1558–1582) he succeed to Wilhelm von Fürstenberg as a Master of the Teutonic Order in Livonia. When the Livonian Confederation came under increasing pressure from Tsar Ivan the Terrible, 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.
On 11 March 1566 Kettler married Anna, Duchess of Mecklenburg, daughter of Duke Albert VII of Mecklenburg-Güstrow and Princess Anna of Brandenburg. After Dukes proposal in 1567 Regional assembly (landtag) took decision to build 70 new churches and 8 schools in the remote areas of Duchy where many peasants still lived and died unbaptized.
- Cruse, Karl Wilhelm (1833). Curland unter den Herzoegen, Vol. 1 (in German). Reyher. p. 64.
- World and Its Peoples. Marshall Cavendish. September 2009. pp. 1047–. ISBN 978-0-7614-7896-6. Retrieved 13 August 2012.
- Bues, Almut (2005). Zones of Fracture in Modern Europe: The Baltic Countries, the Balkans, and Northern Italy. Otto Harrassowitz Verlag. p. 80. ISBN 344-705-119-1.
- Grusemann, Hans, 1990. Die Frühgeschichte des Geschlechts Ketteler (Kettler), 12.-16. Jahrhundert. Soest.
- Schwennicke, Ditleff. Europäische Stammtafeln zur Geschichte der Europäischen Staaten (Neue Folge), Band VIII, Tafel 91 (Die Ketteler).
- Salomon Henning's Chronicle of Courland and Livonia, translated and edited by Jerry C. Smith, William Urban and Ward Jones
- Heinz Matthiesen (1964), "Gotthard Kettler", Neue Deutsche Biographie (NDB) (in German), 6, Berlin: Duncker & Humblot, pp. 678–679; (full text online)
- Theodor Schiemann, Wilhelm Crecelius (1882), "Kettler, Gotthard", Allgemeine Deutsche Biographie (ADB) (in German), 15, Leipzig: Duncker & Humblot, pp. 680–685
| Duke of Courland