Don Quixote is a satire of courtly romantic stories. The character of Don Quixote believes he is a real knight, and he comports himself with all the honor, grace, and bravery that he possibly can. Unfortunately for Quixote, he is not a real knight, and the world around him is not set up to have the adventures expected of a real knight. When he believes he is fighting giants, he is only fighting windmills.
Where a real knight might be expected to have a suit of armor, Don Quixote wears a pot on his head. Instead of a noble steed, he rides on an old, decrepit horse. Rather than a young, capable squire at his side, he is accompanied by his tubby, wise-cracking friend Sancho Panza. And instead of a lovely maiden for his love interest, Quixote devotes himself to Dulcinea del Toboso, a pig-raising prostitute from a nearby town who never appears in the story.
Quixote is a ridiculous, comical figure. The enduring popularity of this character, however, stems from the fact that there is also something very endearing about him. The limitations of the world around him do not stop Quixote from pursuing his dream. On the one hand, Quixote is a man suffering from mental illness in a public, embarrassing fashion. But on the other, through his own perspective, he is a true knight, because he lives up to the ideals of being a knight as well as he possible can.