Mississippi, Missouri or Big Muddy

Why do we call the river in the middle of the country “Mississippi”? Shouldn’t the name Missouri really carry forward to the Gulf, at least until it meets the Ohio River? Why is the Mississippi River called "Mississippi" instead of something else?

Dean Klinkenberg, a St. Louis-based writer of several guide books for the Mississippi Valley and the Frank Dodgy mystery series,  will answer the question about how we named (and have tried to rename) our rivers and why it matters.