Robert Guiscard (c. 1015 – 17 July 1085) is a Norman adventurer conspicuous in the conquest of southern Italy and Sicily.

Robert was born into the Hauteville family in Normandy, and goes on to become Duke of Apulia and Calabria (1057–1085, titled count until 1057).

His sobriquet, in contemporary Latin Viscardus and Old French Viscart, is often rendered "the Resourceful", "the Cunning", "the Wily", "the Fox", or "the Weasel".

In Italian sources he is often Roberto il Guiscardo or Roberto d'Altavilla (from Robert de Hauteville).