The knight-errant who took windmills for giants
Cervantes’s hero, a down-at-heel country gentleman driven mad by chivalric romances, who names himself "Don Quixote," dons rusty armor, and sets out with his plain servant Sancho Panza to do knightly deeds. He takes inns for castles, windmills for giants, peasant girls for noble ladies, and is battered bloody again and again. "Quixotic" became ever after a proper adjective: to throw oneself, headlong, at an ideal out of step with the times and doomed to fail.
The world Don Quixote sees is never the one others see: what to them is a windmill is to him a giant; what to them is absurdity is to him the sublime. Cervantes lets the reader laugh and ache at once — until, by the end, you can no longer tell whether Don Quixote has gone mad, or whether it is the world, with no room for an ideal, that has gone wrong.
Below are how modern works borrow or reinterpret this name or story — not the original material. The two differ, so keep them apart.