Mauricio Carlos de Onís y Mercklein

Mauricio Carlos de Onís y Mercklein (17 September 1790, in Dresden, Kingdom of Saxony – 24 November 1861, in Cantalapiedra, Spain) was a Spanish politician and diplomat who served as Minister of State in 1840 and as President of the Congress of Deputies.

Mauricio was son of Luis de Onís y González-Vara, an important diplomat who signed the Adams-Onís Treaty with the United States in 1819, and of Federika Christina von Mercklein. He married in Cantalapiedra, 11 December 1816, his first cousin Carolina de Onís, and had issue.