Which explorer was the first to explore the southeastern United States?

Hernando de Soto was the first European explorer known for extensively exploring the southeastern region of what is today the United States. His expedition began in 1539 when he landed in Florida and moved through various states including Georgia, South Carolina, North Carolina, Tennessee, Alabama, Mississippi, and parts of Arkansas. De Soto's explorations provided significant insights into the Appalachian Mountain region and the Mississippi River Valley, and he was the first European to cross the Mississippi River. His journey marked a pivotal moment in the history of exploration in North America, as it was one of the earliest instances of a European encountering the cultures and civilizations of the indigenous peoples in the southeastern United States. This established him as a key figure in the early exploration of this area, leading to a deeper understanding of the land and its inhabitants during that time.