Antoniotto Usodimare or Usus di Mare (1416–1462) was a Genoese trader and explorer in the service of the Portuguese Prince Henry the Navigator. Jointly with Alvise Cadamosto, Usodimare discovered a great stretch of the West African coast in two known voyages in 1455 and 1456. They notably discovered the Cape Verde islands, and the Guinea coast from the Gambia River to the Geba River (in Guinea-Bissau)
Antoniotto Usodimare was a prominent merchant and citizen of the Republic of Genoa, a director of the Genoese mint and a shareholder in the Banco di S. Giorgio. However his fortunes soon took a turn for the worse. Around 1450, Usodimare fled Genoa to escape his creditors, making his way first to Seville, and then Lisbon. He eventually entered into the service of Portuguese Prince Henry the Navigator, hoping that by engaging in the profitable Portuguese trade on the West African coast, he might quickly recover his fortunes and pay back his debts.
In some sources, Antoniotto Usodimare is confused with António de Noli, another Genoese explorer in the service of Prince Henry, who, according to the memoirs of Portuguese captain Diogo Gomes, also went to the Gambia River and (re)discovered the Cape Verde islands in 1462. Although the coincidences are interesting, there is no evidence they are the same man.
Antoniotto Usodimare sailed out in early 1455 in a Portuguese caravel, probably supplied by Prince Henry the Navigator, accompanied by another caravel with an unnamed Portuguese squire of the prince. Along the way, in June 1455, around Cape Vert peninsula, he stumbled across Alvise Cadamosto, a Venetian captain also in Henry's service. They joined forces and proceeded to jointly find the mouth of the Gambia River in June 1455. However, meeting strong hostility from the natives upriver, the ships returned to Portugal. It is here that Antoniotto Usodimare wrote his famous letter (dated December 12, 1455) to his creditors back in Genoa, giving a (rather exaggerated) account of his expedition the Gambia, and promising that on his next expedition there, he would make enough money to finally pay them back.