Richard Booth, who turned Hay-on-Wye into a second-hand bookshop capital, has died aged 80.
He was responsible for transforming the market town in Powys into the world's foremost home for books.
Mr Booth - who dubbed himself "king of Hay" opened his first bookshop in the town's former fire station in 1961 and was honoured with an MBE in 2004.
Anne Addyman, from Addyman's Books, said: "This town has become what it is because of him."
Mr Booth kept his own shop until he made the decision to sell it in 2007.
His passion for Hay-on-Wye also led him to proclaim it an independent kingdom on 1 April 1977, crowning himself as monarch and issuing passports to locals.
The self-styled "king of Hay" also issued his own speeches - including at Christmas - and awarded peerages.
Ms Addyman said: "We are absolutely devastated. It feels like we have lost our father, he is such a legend.
"We are going to have black books in the windows and a week of mourning for the king of Hay.
"He was unique. He was the first person to diversify a rural economy, what he did was cutting edge in the 60s and 70s.
"There are now over 50 book towns in the world, Hay is still the best, he was like the emperor of the book town movement as well."
Peter Florence, director of the Hay Festival, said he introduced a lot of people to the idea of antiquarian books and Hay would have "gone under" without his brilliant idea of diversifying beyond just a market town.
"He was genuinely and deeply eccentric," he added.
"There was a time when he first started out when he was a tremendously charismatic, visionary entrepreneur who had great fun. He wasn't really in it for money, he was in it for the craic, for the party and the good times."
Mr Booth was also a regular pamphlet writer and chairman of the Welsh Booksellers Association as well as life president of the International Organisation of Book Towns.
He stood for Socialist Labour for Mid and West Wales in the 1999 Assembly elections and was a friend of trade unionist Arthur Scargill.
On the anniversary of Hay's "independence" on 1 April 2017, Mr Booth reminded people the town had declared itself independent of the EU in 1978 with "Hay's Hexit".
"Hay is now world famous not only for its books and culture, but for the revolutionary spirit of its citizens, who have struggled for 40 years against an overwhelming tide of government bureaucrats, quangos and big business corporations, who have sought to stifle our peoples' originality for the benefit of their own agendas," he wrote.
Listing his recreations for Who's Who, Mr Booth said: "Creating a monarchy in Hay because democracy has vanished and the divine right of kings is an effective opposition to the divine right of the officials; gardening."