Don Quixote is an elderly sixteenth-century Spanish gentleman, unmarried, well-mannered and cultured, whose real name is Alonso Quijana (or Quijano, depending on which film version of "Don Quixote" you are watching). He is the title character of the novel "Don Quixote de La Mancha", by the real-life Spanish author, Miguel de Cervantes y Saavedra (1547-1616). It is considered by many critics to be the greatest novel ever written.
Alonso Quijana's one great passion is books of chivalry, which he reads obsessively, and believes are all true no matter how ridiculous and fantastical their plots are. He finally goes insane from reading too many of them, and, in an era when there are no knights left, decides to become one, renaming himself Don Quixote de la Mancha. As his "squire", he takes along the rather gullible peasant, Sancho Panza. Although he is insane, Don Quixote's intentions (to wipe out evil) are noble and completely sincere.
In Cervantes's original novel, Don Quixote chooses a local farm girl named Aldonza to be his lady Dulcinea. However, Aldonza never actually appears in the novel.
At least two film versions of "Don Quixote" are scrupulously faithful to the extremely long novel, but most of them change some elements of the story radically, and Aldonza does appear in several of them. In "Man of La Mancha", the famous musical inspired by "Don Quixote", she is not a farm girl, but a prostitute who works in a local inn.
"Man of La Mancha" uses a mere fraction of Don Quixote's adventures in its plot, as do other dramatizations of the novel. (The ballet version of "Don Quixote", by Ludwig Minkus, uses only two.) Depending on which film version of "Don Quixote" one watches, different adventures are included - the novel is nearly 1,000 pages long - but the one most famous, which turns up in nearly every adaptation, is Quixote's attack on the windmills, which he believes to be ferocious giants. Another of his famous adventures is that involving the barber and his shaving basin, which Don Quixote takes to be the miraculous helmet of Mambrino.
In "Man of La Mancha", Don Quixote sings the hit song "The Impossible Dream".