Robert Guiscard (; Modern French: [ɡiskaʁ]; c. 1015 – 17 July 1085) was a Norman adventurer remembered for the conquest of southern Italy and Sicily. Robert was born into the Hauteville family in Normandy, went on to become count and then duke of Apulia and Calabria (1057–1059), duke of Sicily (1059–1085), and briefly prince of Benevento (1078–1081) before returning the title to the papacy.

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 II Guiscardo or Roberto d'Altavilla (from Robert de Hauteville), while medieval Arabic sources call him simply Abārt al-dūqa (Duke Robert).