Ernst Casimir I of Nassau-Dietz (Dillenburg, December…

Ernst Casimir I of Nassau-Dietz (Dillenburg, December 22, 1573 – Roermond, June 2, 1632) is the eleventh child of John VI, Count of Nassau-Dillenburg and Elisabeth of Leuchtenberg.

After the death of his father, the county of Nassau had been divided among his five living sons, Ernst Casimir following him as Count of Nassau-Dietz and Stadtholder of Friesland; he had been appointed Stadtholder of Groningen and Drenthe in August 1625.

Primarily known as an outstanding military leader, he has served under Maurice in the siege of the cities of Steenwijk and Oldenzaal, and Frederick Henry, Prince of Orange during the Siege of Groenlo (1627) and the Siege of 's-Hertogenbosch.

As Stadholder of Groningen he founds the Nieuweschans fortress in 1628.

Although he owns little in Friesland, he is popular there, and people grant his heir the right to rule after his death.

The portrait of his wife and children, painted in 1621, is unusual in its lack of modesty.