Denis Diderot (French: [dəni did(ə)ʁo]; 5 October 1713 – 31 July 1784) was a French philosopher, art critic, and writer, best known for serving as co-founder, chief editor, and contributor to the Encyclopédie along with Jean le Rond d'Alembert. He was a prominent figure during the Enlightenment.

Diderot began his education by obtaining a Master of Arts degree in philosophy at a Jesuit college in 1732. He considered working in the church clergy before briefly studying law. When he decided to become a writer in 1734, his father disowned him for not entering one of the learned professions. He lived a bohemian existence for the next decade. He befriended philosopher Jean-Jacques Rousseau in 1742.

Though his work was broad as well as rigorous, it did not bring Diderot riches. He secured none of the posts that were occasionally given to needy men of letters; he could not even obtain the bare official recognition of merit that was implied by being chosen a member of the Académie française. He saw no alternative to selling his library to provide a dowry for his daughter. Empress Catherine II of Russia heard of his financial troubles and commissioned an agent in Paris to buy the library. She then requested that the philosopher retain the books in Paris until she required them, and act as her librarian with a yearly salary.^[3] Between October 1773 and March 1774, the sick Diderot spent a few months at the empress's court in Saint Petersburg.^[4][5]

Diderot died of pulmonary thrombosis in Paris on 31 July 1784, and was buried in the city's Église Saint-Roch. His heirs sent his vast library to Catherine II, who had it deposited at the National Library of Russia. He has several times been denied burial in the Panthéon with other French notables.^[6] The French government considered memorializing him in this fashion on the 300th anniversary of his birth,^[7] but this did not come to pass.