simpleton

Etymology

simple + -ton (as in a surname). Compare French simplet, Italian semplicione.

noun

1. (derogatory) A simple-minded person lacking common sense.
   Baron Cohen’s new creation (and the previous ones, too) has its roots in Groucho characters like Captain Jeffrey T. Spaulding, Otis B. Driftwood, and Prof. Quincy Adams Wagstaff, and the concept of a pompous simpleton running a rogue nation has obvious parallels to Duck Soup’s Rufus T. Firefly, who leads the country of Fredonia to a needless and highly preventable war. May 15, 2012, Scott Tobias, “Film: Reviews: The Dictator”, in The Onion AV Club
   The stranger had crossed a sacred line. He had mentioned the men's mothers. Nothing could get him out of a beating now, even the fact that he was obviously a simpleton. Albeit a simpleton with a good vocabulary. 2001, Eoin Colfer, Artemis Fowl, page 92