Final answer:
Rene-Robert de LaSalle is the explorer who explored the Mississippi River and named Louisiana in honor of King Louis XIV.
Step-by-step explanation:
The explorer who explored the Mississippi River and named Louisiana in honor of King Louis was C. Rene-Robert de LaSalle. La Salle traveled down the Mississippi River in 1670, and unlike Hernando de Soto, who had ventured in the region earlier, La Salle encountered a land that had returned to wilderness after the effects of diseases brought by European explorers. De LaSalle claimed the territory he explored for France and named it Louisiana in tribute to King Louis XIV.