Who was the Italian explorer who figured out that Columbus had not reached Asia?

The Italian explorer who figured out that Columbus had not reached Asia was Amerigo Vespucci. He undertook several voyages to the New World in the late 15th and early 16th centuries and recognized that the lands discovered by Columbus were part of a separate continent, which he referred to as the "New World." His findings were significant enough that the name "America" was later derived from his first name. Vespucci's work helped shift European understanding of geography during that era.