Jean Fonteneau dit Alfonse de Saintonge (also spelled Jean Allefonsce) (born 1484 in Saintonge - died December 1544 or 1549 off La Rochelle) was a French navigator, explorer and corsair, prominent in the European age of discovery.
Born Jean Fonteneau, he married a Portuguese woman named Victorine Alfonse (or Victorina Alfonso), hence his nickname "Alfonse". Taking to the sea at age 12, he joined the Portuguese commercial fleets as they sailed past the seven seas to the coasts of Brasil, Western Africa, and around the Cape to Madagascar and Asia. His writings talk of days lasting three months, possibly suggesting he had approached Antarctica. By the 1540s he was a renowned pilot, leading fleets to Africa and the Caribbean and reputed to have never lost a ship. André Thévet mentions a conversation where Alfonse described looting Puerto Rico as a corsair. It was long thought that the Rabelaisian hero Xenomanes was based on Alfonse.
In 1542-43 Alfonse piloted Jean-François de la Roque de Roberval's attempt to colonize Canada on the heels of Jacques Cartier's third voyage there. Alfonse established that one could sail through a passage between Greenland and Labrador. The crew of 200, including prisoners and a few women, spent a harsh winter on the shores of the St. Lawrence River, hit by scurvy and losing a quarter of the colonists before sailing back to France.
In late 1544, Alfonse left La Rochelle with a small fleet and disrupted Basque shipping, while the treaty of Crépy had just been signed between France and Spain. A Spanish fleet led by Pedro Menéndez de Avilés caught up to him as he was getting back to La Rochelle and killed him at sea. Some sources say this fatal encounter occurred in 1549.
His writings were published as Les voyages avantureux du Capitaine Ian Alfonce (1559), the Rutter of Jean Alphonse (1600) and La cosmographie avec l’espère et régime du soleil du nord par Jean Fonteneau dit Alfonse de Saintonge, capitaine-pilote de François Ier (1904). In them he describes the various places and peoples he and others have seen, many of them for the first time in print (such as Gaspé, the Beothuk, Saint-Pierre Island, the jewels of Madagascar, a continent south of Java) and provides navigational instructions on how to get there.