Both North and South America were named after Amerigo Vespucci, an Italian explorer and cartographer who sailed to the West Indies and South America several times between 1497 and 1504. German clergyman and mapmaker Martin Waldseemüller affixed Vespucci's name to the "New World" in 1507.
Amerigo Vespucci is widely recognized as the first explorer to realize that North and South America were new continents distinct from the Asian land mass. This is the main reason why several 16th century mapmakers justified naming the bodies of land after him, rather than after the previous discoverer, Christopher Columbus. Waldseemüller's original map only named South America after the Italian explorer, but in 1538, the mapmaker Gerardus Mercator became the first to formally name both new continents after Vespucci.