Dirck Volckertszoon Coornhert, also known as Theodore Cornhert, was a Dutch writer, philosopher, translator, politician, theologian and artist. Coornhert is often considered the Father of Dutch Renaissance scholarship.

Coornhert was the youngest son of Volckert Coornhert, an Amsterdam cloth merchant. As a child he spent some years in Spain and Portugal. Returning home, he was disinherited by his father's will in 1539, for his marriage with Cornelia (Neeltje) Simons, a portionless gentlewoman from Haarlem, whose sister was Anna Simonsdr, the mistress of Reginald (Reinoud), count of Brederode (they were the parents of Lucretia van Brederode). He was only seventeen and she was twelve years older. Through his sister-in-law, he became major-domo to Reginald at his castle in Vianen for a short time. Soon after that, in 1541, he bought a house in his wife's home town of Haarlem on the St. Janssteeg from Anna and her husband Jan. Though he started off working for Reginald, he lived near the school where the St. Jan commanderij taught classic works and commissioned art. Maarten van Heemskerck had just returned from Italy and impressed Coornhert with his work. Coornhert became an engraver on copper, and produced works in collaboration with Heemskerck which became popular.

After learning Latin in 1552, Coornhert published Dutch translations from Cicero, Seneca and Boethius. His 1562 translation of the first twelve books of Homer's Odyssey is one of the first major works of Dutch Renaissance poetry. He was appointed secretary to the city of Haarlem (1562) and secretary to the burgomasters (1564). Throwing himself into the struggle against Spanish rule, he drew up the manifesto of William the Silent, Prince of Orange (1566).

Imprisoned at the Hague in 1568, he escaped to Cleves, where he maintained himself by his art. Recalled in 1572, he was for a short time secretary of state in the Dutch Republic; his aversion to military violence led him to return to Cleves, where William continued to employ his services and his pen. Possibly inspired by his time in jail, he wrote a book "Boeventucht" on the causes of crime with ideas for more humane methods of punishment and correction.