Marie de Flavigny, Countess of Agoult (1805-1876), was a French writer and historian, known by her pseudonym Daniel Stern. She was born in Frankfurt am Main and died in Paris. She had a notable relationship with Franz Liszt, with whom she had three children, including Cosima Wagner. She was an influential figure in the literary and political circles of her time, author of works such as "Nélida" (a novel with autobiographical elements) and "Histoire de la Révolution de 1848".