Short answers, pulled from the story.
Denis Diderot was a French philosopher, art critic, and writer born in Langres, Champagne on the 5th of October 1713. He is best known as co-founder and chief editor of the Encyclopédie, the first encyclopedia to name its contributors and to describe the mechanical arts, which he co-created with Jean le Rond d'Alembert beginning in 1751.
Diderot was arrested on the 24th of July 1749 and imprisoned in solitary confinement at the Vincennes fortress after being identified as the anonymous author of the Letter on the Blind, an essay that argued against the existence of a providential God. He had been under police surveillance since 1747. He was released on the 3rd of November 1749 after writing a letter of submission to the governor.
In 1766, Catherine the Great bought Diderot's personal library of 3,000 volumes for 15,000 livres, appointed him its custodian at an annual salary of 1,000 livres, and paid him fifty years of that salary in advance. She later gave him 3,000 rubles to cover the cost of his journey to Saint Petersburg in 1773-1774, plus an expensive ring and a military escort home.
The French government formally suppressed the Encyclopédie in 1759, but the work continued clandestinely. Jean le Rond d'Alembert and other prominent contributors withdrew, leaving Diderot as sole editor. The final 28 folio volumes were delivered to subscribers in 1772, twelve years after the project had been banned. Diderot later discovered that the printer Le Breton had secretly removed passages he considered too dangerous, destroying the original manuscripts to prevent detection.
Several of Diderot's most celebrated works were published posthumously. Rameau's Nephew was written between 1761 and 1774 and not published until Goethe translated it into German in 1805; the original French manuscript was not found until 1891. La Religieuse appeared in 1796, Jacques le fataliste in 1796, and Paradox of the Actor in 1830.
L'esprit de l'escalier, meaning the experience of thinking of the perfect reply only after a conversation is over, originates in Diderot's theatrical essay Paradox of the Actor, written between 1770 and 1778. The essay was published posthumously in 1830. The phrase has since entered common use in both French and English.