Context : Friedrich Kettler (Latvian: Frīdrihs Ketlers, 25 November 1569 in Mītava (German Mitau, now Jelgava) -- 17 August 1642) was Duke of Courland (Latvian: Kurzeme, now part of Latvia) from 1587 to 1642. 
Subject : Friedrich Kettler 
Relation : spouse
What is Friedrich Kettler's spouse's name?