Otto, Hereditary Prince of Hesse-Kassel

Otto was the eldest son of Landgrave Maurice of Hesse-Kassel (1572-1632)^[1] from his marriage to Agnes (1578-1602), the daughter of Count John George of Solms-Laubach (1546–1600) and his wife, Margaret of Schönburg-Glauchau (1554–1606). Poet Hermann Kirchner, later professor of rhetoric at the University of Marburg, wrote a poem to mark Otto's birthday.^[2] The Ottoneum, built in Kassel by Maurice in 1603, was the first theater building constructed in Germany. Maurice named it after his son.

Otto and his siblings were educated by his father. In 1606 he became the lay administrator of Hersfeld Abbey, which by then was a Lutheran institution. After completing his studies at the University of Marburg, Otto made a Grand Tour. He was in England from 23 June to 7 August 1611, with a retinue of about thirty, and was among the potential suitors of Princess Elizabeth.^[3] (She later married Otto's second cousin Frederick V of the Palatinate.) As Otto's father was known as a skilled composer, music played a large part of the entertainment. John Milton, the poet's father, composed a song in four parts, for which the landgrave presented him with a gold medal.^[4]

When he returned, his father involved him in the business of government.

In 1617, he suffered from the German measles. He had a fever and from his sickbed, he tried to shoot a barking dog, which annoyed him. He missed so badly that he hit himself in the chest and died. He was buried in the Lutheran St. Mary's church in Marburg.

In Kassel on 24 August 1613 Otto married firstly princess Catherine Ursula of Baden-Durlach (b. Schloss Karlsburg, 19 June 1593 - d. Marburg, 15 February 1615), daughter of George Frederick, Margrave of Baden-Durlach. She died after giving birth a still-born son.

In Dessau on 14 June 1617 Otto married secondly Princess Agnes Magdalene of Anhalt-Dessau (b. Dessau, 29 March 1590 - d. Eschwege, 24 October 1626), daughter of John George I, Prince of Anhalt-Dessau. This marriage was childless.

Otto left a son born out of wedlock with an unknown woman:

• Ernest Reinhard von Hattenbach (b. posthumously Hachborn, 17 December 1617 - d. Rodenberg, 1 April 1694), married in 1669 lady in waiting to Landgravine Hedwig Sophie, Anna Katharina von Hake (1650-1707), daughter of Daniel von Hake zu Klein-Machnow (1582-1648) and his second wife, Brigitte von der Gröben. They had issue

• Christian Röth: Geschichte von Hessen p. 255 ff
• Christoph von Rommel: Geschichte von Hessen p. 324 ff