Final answer:
Hernando de Soto is known as the first European to extensively travel through what is now southeast North America.
Step-by-step explanation:
The first European to extensively travel through what is now southeast North America was Hernando de Soto. He was a Spanish explorer who embarked on an expedition through the southeastern part of the United States, including what is today Florida, Georgia, and Alabama, among other states. His journey, which took place between 1539 and 1542, was significant in the history of European exploration of the Americas.
While other well-known explorers such as Christopher Columbus, Amerigo Vespucci, and Pedro Cabral played pivotal roles in the exploration of the New World, it was Hernando de Soto who extensively explored the southeastern region of North America. Additionally, Columbus is most widely known for his voyages that led to the European awareness of the American continents, Vespucci for realizing the new landmass was not Asia but a separate continent, leading to the name "America" derived from his first name. Pedro Cabral is credited with reaching Brazil and claiming it for Portugal.