Cornhert, Or Coornhert, Diedcrik, a Dutch author, born in Amsterdam in 1522, died in Gouda in October, 1590. He was for a while steward in the service of a nobleman, and afterward learned the art of an engraver. In 1564 he was appointed secretary to the burgomasters of Haarlem, and assisted in preparing the way for the establishment of the independence of Holland. He was the author of the manifesto published by William prince of Orange in 1566, and for this he was afterward thrown into prison at the Hague. When he gained his liberty he was compelled to retire to Cleves, where he earned a livelihood as an engraver. He was recalled to Holland in 1572, and appointed secretary of state, but, having made himself obnoxious to the principal generals by his attempts to check the disorderly conduct of the army, was again exiled. He afterward returned, and though he offended many by his theological views, he finally, died in peace in his native land. He wrote in defence of the conduct of the Dutch in rebelling against the king of Spain, asserting that in doing so they only obeyed the law of self-defence. He wrote a poem "On the Use and Abuse of Fortune," and is said to be the author of Wilhelmus van Nassouwen, a national song very popular in Holland. Just before his death he wrote an essay against putting heretics to death.

His works were published at Amsterdam in 1630, in 3 vols. fol.