Juan Díaz de Solís (ca. 1470-1516), the pilot major of Castile, sailed under the Spanish flag to explore the Americas, where he discovered the Río de la Plata.

Juan Díaz de Solis was evidently born in Portugal, although his ancestry was Spanish. As a young man, he visited India perhaps several times as a seaman in Portuguese service. Dissatisfied with his meager and often unpaid wages, he served for a time with French corsairs. When he and his French associates captured a Portuguese caravel returning from the Gold Coast, this made his return to Portugal impossible, so he transferred his services to Spain. He had by this time become a skilled pilot.

Solís was in Spain by 1508, and in that year he embarked on a discovery voyage with Christopher Columbus's former companion Vicente Yáñez Pinz...