Who was the Jesuit priest who accompanied Louis Jolliet?

Answer 1

Jacques Marquette, S.J. was a missionary Jesuit priest who explored the Mississippi River with Louis Jolliet, a young man who was in minor Orders.

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from The Catholic Encyclopedia:

Jesuit missionary and discoverer of the Mississippi River, b. in 1636, at Laon, a town in north central France; d. near Ludington, Michigan, 19 May, 1675. He came of an ancient family distinguished for its civic and military services. At the age of seventeen he entered the Society of Jesus, and after twelve years of study and teaching in the Jesuit colleges of France was sent by his superiors (1666) to labour upon the Indian missions in Canada. Arriving at Quebec he was at once signed to Three Rivers on the Saint Lawrence, where he assisted Druillettes and, as preliminary to further work, devoted himself to the study of the Huron language. Such was his talent as a linguist that he learned to converse fluently in six different dialects.

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So far had he gone in his preparations for the trip that he sent presents to the neighbouring pagan tribes and obtained permission to pass through their country. However, before he could carry out his designs the Hurons were forced to abandon their village at La Pointe on account of a threatened attack of the Dakotas. The missionary embarked with the entire tribe and followed the Indians back to their ancient abode on the north-west shore of the Straits of Mackinac. Here a rude chapel was built and the work of instructing the Indians went on. There is extant a long letter from his pen in which Marquette gives some interesting accounts of the piety and habits of the converted Hurons (Jesuit Relations, LVII, 249). But Marquette was yearning for other conquests among the tribes which inhabited the banks of the Mississippi. He concluded this letter with the joyful information that he had been chosen by his superiors to set out from Mackinac for the exploration which he had so long desired. In the meanwhile accounts of the Mississippi had reached Quebec, and while Marquette was preparing for the voyage and awaiting the season of navigation, Joliet came to join the expedition. On 17 May, 1673, with five other Frenchmen, in two canoes, Marquette and Joliet set forth on their voyage of discovery.