Who was the first white explorer to cross into Oklahoma?

The correct answer is Coronado. Francisco Vázquez de Coronado was a Spanish explorer who led an expedition into the North American territories in the 1540s, specifically in search of the mythical Seven Cities of Gold. During his journey, he became one of the first European explorers to travel into what is now known as Oklahoma. His expedition ventured through various regions including parts of the southern Great Plains, and while he did not specifically explore the entire area of modern Oklahoma, his claims to exploring this territory mark him as a significant figure in the region's history.

The other explorers listed did not cross into Oklahoma in the same manner. For instance, Hernán Cortés primarily focused his exploits in Mexico and did not venture north into what is now the United States. Similarly, Hernando de Soto explored the southeastern United States, including parts of Florida and beyond, but did not specifically document crossing into the territory that would later become Oklahoma. Mendoza, while a notable figure, is less recognized for exploration in North America and is not directly related to the exploration of Oklahoma. This context is crucial in understanding why Coronado is acknowledged as the first white explorer to enter Oklahoma.