Excerpts from Books and Wikipedia
"He was Napoleon's chief diplomat during the years when French military victories brought one European state after another under French hegemony, as, he believed, they rightfully should be. . . . He played a major role at the Congress of Vienna in 1814–1815, where he negotiated a favourable settlement for France and played a role in decisions regarding the undoing of Napoleon's conquests.
Talleyrand polarizes scholarly opinion. Some regard him as one of the most versatile, skilled and influential diplomats in European history, and some believe that he was a traitor, betraying in turn the Ancien Régime, the French Revolution, Napoleon, and the Restoration." [Wikipedia]
"Talleyrand, who presided over French foreign policy from 1814 to 1835, remains the model for the French diplomat to this day." [Hobsbawm: Revolution, p. 100]