the hero of a romance by Cervantes; chivalrous but impractical
any impractical idealist (after Cervantes' hero)
Any person or character who displays quixotism.
A famous 1605–1615 Spanish novel by Miguel de Cervantes (1547–1616), whose full title is El ingenioso hidalgo don Quijote de la Mancha (The Ingenious Gentleman Don Quixote of La Mancha).