Marco Sanudo (c. 1153 Eraclea – between 1220 and 1230, most probably 1227) was the creator and first Duke of the Duchy of the Archipelago, in Italian: "Duca del Mare Egeo e Re di Candia", Barone delle Isole di Nasso, Pario, Milo, Marine ed Andri, duchy granted by the Republic of Venice to him and all his descendants. After the Fourth Crusade his lineage became named Sanudo de Candia.

Maternal nephew of Venetian doge Enrico Dandolo, he was a participant in the Fourth Crusade (1204). He was part of the negotiations when the Republic of Venice bought the island of Crete from Boniface of Montferrat.

Between 1205 and 1207, or a little after 1213-1214, he gathered a fleet and captured the island of Naxos, laying the foundations of the Duchy of the Archipelago. He built a new capital city on the island, Kastro (now the main port). During his reign, he blended the Byzantine and Venetian organizations.

He became vassal of the Latin Emperor Henry of Flanders around 1210 or 1216. For his lord, he fought against the Empire of Nicaea. But for Venice, he took part in the Cretan expedition of 1211.

All biographies of Marco Sanudo were written in the centuries after the facts they tell. Most of them are Venetian chronicles dating from the 14th and 15th centuries. In the first one, Istoria di Romania, Marino Sanudo Torsello, a member of the Sanudo family, writes about Marco Sanudo only this:

he conquered the islands.

Doge Andrea Dandolo wrote a history of Venice (called Chronica extensa) around 1350. This text is the first to relate the conquest of the Aegean islands and has been the foundation of all later accounts:

Sailing separately, Marco Sanudo and those following him conquered the islands of Naxos, Paros, Milos and Santorini, and Marino Dandolo conquered Andros. Also, Andrea and Geremia Ghisi [took] Tinos, Mykonos, Skyros, Skopelos and Skiathos.