Fernando de Soto
Hernando de Soto (Jerez de los Caballeros, Badajoz, Spain, c. 1496/1497–May 21, 1542) was a Spanish explorer and conquistador who, while leading the first European expedition deep into the territory of the modern-day United States, was the first European to discover the Mississippi River.
Benson John Lossing, ed. Harper's Encyclopedia of United States History (vol. 3) (New York, NY: Harper and Brothers, 1912)