“The world has lost one of its brightest, sharpest minds,” said Larry Finlay of his publishers Transworld.
The author died at home, surrounded by his family, “with his cat sleeping on his bed”, he added.
Sir Terry wrote more than 70 books during his career and completed his final book last summer.
He “enriched the planet like few before him” and through Discworld satirised the world “with great skill, enormous humour and constant invention,” said Mr Finlay.
“Terry faced his Alzheimer’s disease (an ’embuggerance’, as he called it) publicly and bravely,” said Mr Finlay.
“Over the last few years, it was his writing that sustained him. His legacy will endure for decades to come.”
Sir Terry leaves wife Lyn and daughter Rhianna.
The announcement of his death was made on Sir Terry’s Twitter account on Thursday afternoon, with Rhianna later writing: “Many thanks for all the kind words about my dad. Those last few tweets were sent with shaking hands and tear-filled eyes.”
Despite campaigning for assisted suicide after his diagnosis, Sir Terry’s publishers said he did not take his own life.
BBC News correspondent Nick Higham said: “I was told by the publishers his death was entirely natural and unassisted, even though he had said in the past he wanted to go at a time of his own choosing.”
Fellow author and friend Neil Gaiman was among those paying tribute to Sir Terry, writing on his website: “There was nobody like him. I was fortunate to have written a book with him, when we were younger, which taught me so much.”
Gaiman added: “I will miss you, Terry, so much.”
Actor Sir Tony Robinson described his friend as a “bit of a contradiction”, saying: “He was incredibly flamboyant with his black hat and urban cowboy clothes.
“But he was also very shy, and happiest with his family
“Everybody who reads his work would agree Death was one of his finest creations – Terry in some way has now shaken hands with one of his greatest-ever creations.”
Prime Minster David Cameron said: “Sad to hear of Sir Terry Pratchett’s death, his books fired the imagination of millions and he fearlessly campaigned for dementia awareness.”
The Discworld series – which started in 1983 – was based in a flat world perched on the backs of four elephants which, in turn, stand on the back of a giant turtle.
By 2013, he had written more than 40 instalments.
At the peak of his writing powers, Sir Terry – known for his striking dress sense and large black fedora – was publishing more than three books a year. His quirky and satirical view of the world won him a worldwide following.
At the turn of the century, he was Britain’s second most-read author, beaten only by JK Rowling.
In August 2007, it was reported Sir Terry had suffered a stroke, but the following December he announced that he had been diagnosed with a very rare form of early-onset Alzheimer’s disease which, he said, “lay behind this year’s phantom stroke”.
Knighted in 2009, he said: “It would appear to me that me getting up and saying ‘I’ve got Alzheimer’s’, it did shake people.”
“The thing about Alzheimer’s is there are few families that haven’t been touched by the disease.
“People come up to me and talk about it and burst into tears; there’s far more awareness about it and that was really what I hoped was going to happen.”
His death was announced on his Twitter account with a tweet composed in capital letters – which was how the author portrayed the character of Death in his novels – read: “AT LAST, SIR TERRY, WE MUST WALK TOGETHER.”
A fundraising site set up in Sir Terry’s memory to raise money for a charity that cares for those with Alzheimer’s has already raised thousands of pounds.
Source :BBC NEWS