A childhood love of adventure eventually led the Belgian Jesuit priest Father Pierre-Jean De Smet to become a missionary to the Indians of the Rocky Mountains. He traveled throughout the northern Rockies, along the way celebrating the first Catholic Mass in what’s now Wyoming on July 5, 1840, during the Green River Rendezvous. In 1851, members of his party named Lake De Smet for him as they traveled from the Missouri River in present Montana to assist in treaty negotiations with the plains tribes near Fort Laramie.