If you go by the original novel by Cervantes, Don Quixote would be a very anti-D&D tale - it was a satire on popular knight novels, and on people using them for escapism and romanticizing about an age of chivalry and heroic deeds that never was.
The literary Don Quixote was an elderly man whose brain has dried out for spending too much time reading books and too little time sleeping, and he is a pretty picaresque character misapplying remembered bits and pieces and trivia from his studies. I would therefore make him a Factotum - Int-based, strong on using skills and odd bits, and all over the place without ever mastering a field.