Isaac Dorislaus (1595 in Alkmaar, Holland – 2 May 1649 at The Hague, Holland) was a Dutch Calvinist historian and lawyer who was an important official in Oliver Cromwell's period of rule. He came to England as a historian. His lectures were seen as political rhetoric, with references to kings with unjustified power aimed at portraying reigning monarch, Charles I of England, as a tyrant. Little was done about his propagandizing however. Dorislaus became advocate general of the army in the first civil war, and for all his previous theorizing about ancient liberties, quickly showed authoritarian tendencies by his attempted introduction of martial law to help him root out Royalists. He is remembered for his part in the High Court of Justice for the trial of Charles I, although his role was not prominent, and being assassinated by Royalists while on a diplomatic mission in his native country. Dorislaus, a Hollander in English service, was appointed by Parliament as ambassador in addition to Strickland. A few days after his arrival he was murdered by Royalists seeking to avenge Charles I's death Background and influence From a strongly Calvinist family, he was educated at Leiden, He arrived in England as the University of Cambridge's first ever professor of History. From the outset he attacked the legitimacy of kings and justified revolt, as when he emphasized the Anglo-Saxon roots of England before 1066, emphasizing what he saw as democratic freedom enjoyed by all Englishmen before they lost it to the Norman conquerors and also justified the Dutch uprising against Spain. His apparent propagandizing for republicanism and regicide was seen as aimed at the King Charles I of England, who was suspected of Catholic sympathies and failure to uphold the country's interests against powerful foreign enemies. Despite his thinly veiled condemnation of the reigning royal power, little real action was taken against him apart from his doctorate being delayed. In 1629 he was admitted a commoner of the College of Advocates. In 1632 he made his peace at court, and on two occasions acted as judge advocate, in the Bishops War of 1640 and in 1642 in the army commanded by the Earl of Essex. Despite his early advocacy of freedom from untrammeled power, once ensconced in a position of authority, Dorislaus attempted to sweep away legal protection for the accused. He assisted in preparing the charge of high treason against Charles I,