Frederick I, Duke of Saxe-Gotha-Altenburg

Frederick I
Frederick I
	Portrait attributed to Christian Schilbach, 1711
Duke of Saxe-Gotha-Altenburg
Reign	26 March 1675 – 2 August 1691
Predecessor	New creation
Successor	Frederick II
Born	15 July 1646; Gotha, Duchy of Saxe-Gotha
Died	2 August 1691 (aged 45); Friedrichswerth
Spouse	; Magdalena Sibylle of Saxe-Weissenfels (m. 1669; died 1681) ; Christine of Baden-Durlach (m. 1681)
Issue	Anna Sophie, Princess of Schwarzburg-Rudolstadt; Dorothea Marie, Duchess of Saxe-Meiningen; Frederick II; Johanna, Duchess of Mecklenburg-Strelitz;
House	Saxe-Gotha-Altenburg
Father	Ernst I, Duke of Saxe-Coburg-Altenburg
Mother	Elisabeth Sophie of Saxe-Altenburg
Religion	Lutheran

Frederick I, Duke of Saxe-Gotha-Altenburg (German: Friedrich I. von Sachsen-Gotha-Altenburg; 15 July 1646 – 2 August 1691), was a territorial ruler in Thuringia from the Ernestine branch of the House of Wettin. He continued the line of Saxe-Gotha founded by Ernest I, his father, which, to distinguish it from the older Gotha line, is generally referred to as Saxe-Gotha-Altenburg.