Miguel de Cervantes' book Don Quixote - regarded as the first modern novel - is still a global bestseller and source of inspiration, 400 years after it was published.
Colin Firth starred as Donovan Quick in the BBC's adaptation
Since 1605, it has been interpreted in a huge number of ways and today it is reputed to be the most widely read and translated book on the planet after the Bible.
The 400th anniversary of the tale of an eccentric knight errant and his long-suffering squire Sancho Panza has also prompted a spate of new editions of the book.
They include one in Spanglish by Ilan Stavans, Professor of Latin American and Latino Culture at Amherst College in Massachusetts.
Professor Stavans is one of the world's major experts on Don Quixote.
He told the BBC World Service's Outlook programme that the book's enduring appeal was down to a central character who "moves across history, presenting different masks, and being appreciated - sometimes as a madman, sometimes as an idealist.
"It is a character that not even Cervantes himself imagined to be so elastic."
Don Quixote is the story of a Spanish man who believes he is a knight, and covers his adventures as he rights wrongs, mistakes peasants for princesses, and - establishing an expression - "tilts at windmills," believing them to be evil giants.
The book was originally published in two parts - it is the anniversary of the first part, El ingenioso hidalgo Don Quijote de la Mancha, that is celebrated this year.
A fake sequel was published by somebody using the pen-name Alonso Fernández de Avellaneda before Cervantes' second part, Segunda parte del ingenioso caballero Don Quijote de la Mancha, was printed in 1614.
Cervantes responded by including an impostor in the second part, as well as ending with Don Quixote's death - to avoid any more "unofficial" sequels.
The book was originally regarded as a comic novel. But this interpretation was radically revised during the French Revolution.
Quixote's appeal is that he "really transcends the circumstances into which he was born, or created," Professor Stavans said.
"You could approach Don Quixote from the American perspective, or the French, or the Soviet - and each individual in those contexts would be able to understand him and identify him."
In the communist Soviet Union, Don Quixote was perceived as a rebel anti-capitalist hero.
He was embraced as the "perfect symbol to fight the capitalist society on the other side of the iron curtain," Professor Stavans stressed.
But he added that, seemingly paradoxically, Don Quixote can also be seen as representing exactly the opposite ideology.
He described him as the "ultimate representation of the American Dream, which will make the individual be at the very core of society."
'Curse of Don Quixote'
The book's enduring popularity is reflected not only in the sheer number of translations and editions, but the number of efforts to bring it to other media - despite a superstition that any adaptations are doomed to failure.
Legendary director Orson Welles spent 20 years trying, but never succeeded. And Monty Python creator Terry Gilliam's effort, starring Johnny Depp, suffered logistical problems that included filming being constantly disrupted by US aircraft taking off and the set being washed away.
Gilliam's attempt eventually became a documentary, Lost In La Mancha, although his actual film project remains stalled.
Terry Gilliam suffered from "the curse of Don Quixote"
Other adaptations include a musical, Man of La Mancha, and a recent BBC TV adaptation, Donovan Quick, which featured Colin Firth railing against the Windmill Bus Company.
Other famous fans of the book include Nobel prize-winning novelist William Faulkner, who read it every year, and former Spanish Prime Minister Felipe Gonzalez, who peruses it daily.
Professor Stavans also pointed out that psychiatrists are big fans, as they "adore the fact that the most enduring of literary characters is a madman".
However he pointed out the end of the novel rebels against psychiatry, suggesting that "madmen might have more wisdom than the actual psychiatrists that are trying to limit their behaviour".
Professor Stavans also added that he personally loves the ending, in which Don Quixote, on his deathbed, realises everything was lunacy - and wants to be remembered as Alonso Quijano, his original name.
"Until the end, he is, for Cervantes, still Don Quixote," Professor Stavans said.
"It's such a compassionate, moving scene that makes the character die - but also remain alive.
"That's probably one of the reasons why he's still with us."