"he posed as a sort of Marat"
Death of Marat by Jacques-Louis David
(1743-1793), despite being best known as a political leader during the French Revolution, was not actually French, nor originally a politician. He was born in Prussia, in Neuchâtel (now a part of Switzerland) and trained as a doctor in Paris, although he didn't gain any qualifications at this time. After he moved to England around 1765 he became acquainted with Voltaire and grew more interested in radical politics. His reputation as a doctor grew after he published an essay on gonorrhea, and the University of St Andrews in Scotland offered him an honourary degree. He moved back to Paris in 1776, where he worked as a court doctor to the aristocracy.
As the Revolution loomed, Marat put aside his career in order to become a political journalist. He was frequently forced into hiding. After the Revolution he was elected to the newly-formed National Convention in 1792 as one of Paris's representatives. He fought against the Girondins alongside Robespierre in order to prevent France from declaring war against Prussia.
Marat was killed on the 13th July 1793 when a young woman, Charlotte Corday, stabbed him to death while he was in the bath.