Amerigo Vespucci (Florence 1451 - Seville 1512) was a merchant/explorer who claimed that he had discovered America. The "New World", America, was named after Vespucci. The name "America" was adopted by South America and gradually expanded to include North America as well. Amerigo traveled to the New World in 1499 landing in the northeastern portion of South America and voyaged again in 1502. He is credit as being the first person to realize that he was landing on a new continent and not a part of Asia.
The alternative theory is that America was named after Richard Americk, one of the backers of John Cabot's voyage of discovery to the new world.
While on one of his voyages, Vespucci wrote two letters to a friend in Europe. He described his travels and was the first to identify the New World of North and South America as separate from Asia. (Columbus thought he had reached Asia to the day he died.)
Amerigo Vespucci also described the culture of the indigenous people, and focused on their diet, their religion, and their sexual, marriage, and childbirth practices. The letters were published in many languages and were distributed across Europe, selling much better than Columbus' diaries.