Balboa, Vasco Núñez de (1475–1517), a Spanish explorer. He was the first European to discover that a great ocean, the Pacific, lay west of the Americas. About 1500 Balboa left Spain on an expedition to explore the Caribbean, and he eventually settled on the island of Hispaniola. In 1510, after a failed farming venture, he stowed away on a ship sailing to reprovision an exploration party on the South American mainland. The expedition had been devastated by disease, starvation, and Indian attacks, and at Balboa's suggestion it went to the relative safety of Darien, an area on the Isthmus of Panama, and founded a colony there. The explorers then appointed Balboa their leader.

To gain new land and wealth, Balboa led 190 Spanish soldiers and 1,000 Indian allies across the isthmus to explore and conquer. From a hilltop Balboa sighted the Pacific on September 25, 1513. Four days later he reached the shore and claimed the ocean and the lands it touched for Spain. He called the ocean the South Sea.

For his discovery, Balboa was appointed governor of the newly discovered lands adjacent to the Pacific. However, enemies at the Spanish court succeeded in placing Pedrarias Dávila in charge at Darien. Balboa was organizing an expedition for the conquest of Peru when Dávila arrested him on a charge of treason and had him put to death.