Final answer:
Christopher Columbus is mostly credited with discovering the Americas in 1492, but it was Amerigo Vespucci who realized they were a separate continent, leading to the naming of 'America' in 1507.
Step-by-step explanation:
The individual most commonly credited with discovering the Americas is Christopher Columbus. Although Norse explorer Leif Erikson reached North America around 1000 CE, Columbus's voyages, beginning in 1492, are traditionally cited as the discovery moment due to them leading to sustained contact between Europe and the New World. It was after Columbus made landfall in the Bahamas that European exploration and colonization of the Americas truly began.
Columbus initially believed he had reached the Indies and referred to the indigenous people he encountered as "Indios," a term that has evolved to "Indian." Despite Columbus's belief that he had found a route to Asia, it was Amerigo Vespucci who recognized that the lands Columbus stumbled upon were part of a separate continent. This led to the naming of the continents as "America" after Vespucci by cartographer Martin Waldseemuller in 1507.