Lewis Carroll became famous by writing Alice in Wonderland. I don't know what story he told, but the first time he told any of his stories was on a boating trip. :-)
The expedition's goal as stated by President Jefferson was "to explore the Missouri River, & such principal stream of it as, by its course & communication with the water of the Pacific ocean...
Most likely, for writing The Chronicles of Narnia (especially The Lion, the Witch and the Wardrobe). During his life he was very well-known as a Christian apologist, also.