Baron Jacques d'Adelswärd-Fersen (20 February 1880 – 5 November 1923) was a French novelist and poet.
His life forms the basis of a fictionalised biography by Roger Peyrefitte.
In 1903 a scandal involving school pupils made him persona non grata in the salons of Paris, and dashed his marriage plans; after which he took up residence in Capri in self-imposed exile with his long-time lover, Nino Cesarini.
He became a "character" on the island in the inter-war years, featuring in novels by Compton MacKenzie and others.
His house, Villa Lysis, remains one of Capri's tourist attractions.