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Armand Jean du Plessis, 1st Duke of Richelieu (French:; 9 September 1585 – 4 December 1642), known as Cardinal Richelieu, was a French Catholic statesman and prelate who had an outsize influence in civil and religious affairs. He became known as l'Éminence Rouge (English: " the Red Eminence "), a term derived from the title "Eminence" applied to cardinals and their customary red robes.

Consecrated a bishop in 1607, Richelieu was appointed Foreign Secretary in 1616. He continued to rise through the hierarchy of both the Catholic Church and the French government, becoming a cardinal in 1622 and chief minister to King Louis XIII of France in 1624. He retained that office until his death in 1642, when he was succeeded by Cardinal Jules Mazarin, whose career the cardinal had fostered. Richelieu became engaged in a bitter dispute with Marie de Médici, the king's mother, and formerly his close ally.

Richelieu sought to consolidate royal power and restrained the power of the nobility in order to transform France into a strong centralized state. In foreign policy, his primary objectives were to check the power of the Habsburg dynasty (reigning notably in Spain and Austria) and to ensure French dominance in the Thirty Years' War of 1618–1648 after that conflict engulfed Europe. Despite suppressing the Huguenot rebellions of the 1620s, he made alliances with Protestant states like the Kingdom of England and the Dutch Republic to help him achieve his goals. However, although he was a powerful political figure in his own right, events such as the Day of the Dupes (French: Journée des Dupes) in 1630 showed that Richelieu's power still depended on the king's confidence.

An alumnus of the University of Paris and headmaster of the College of Sorbonne, Richelieu renovated and extended the institution. He became famous for his patronage of the arts and founded the Académie Française, the learned society responsible for matters pertaining to the French language. As an advocate for Samuel de Champlain and New France, he founded (1627) the Compagnie des Cent-Associés; he also negotiated the 1632 Treaty of Saint-Germain-en-Laye under which Quebec City returned to French rule after English privateers took it in 1629. He was created Duke of Richelieu in 1629.