British author Terry Pratchett speaks after delivering a petition on behalf of the Alzheimer's Research Trust to 10 Downing Street in London, in this November 26, 2008 file photograph. [Photo/Agencies]

GIANT TURTLE

Prime Minister David Cameron said on Twitter: "His books fired the imagination of millions and he fearlessly campaigned for dementia awareness".

Literary figures also expressed their sadness. Canadian author Margaret Atwood wrote: "I vastly enjoyed his playful, smart Discworld books."

His publishers said the world had lost "one of its brightest, sharpest minds". "In over 70 books, Terry enriched the planet like few before him," said Larry Finlay, managing director at Transworld, a division of Penguin Random House.

"As all who read him know, Discworld was his vehicle to satirise this world. He did so brilliantly, with great skill, enormous humour and constant invention," he said.

A unique creation, Discworld is a circular world set on the backs of four elephants standing on the shell of a giant turtle, populated by a vast and colourful cast of characters inspired by the worlds of fantasy, folk tales and mythology.

Pratchett used Discworld to parody those genres, but also to send up aspects of modern life by drawing often incongruous connections between his imaginary world and things ordinary people living in 20th century Britain would recognise.

Selections of Pratchett's quotes quickly appeared on British newspaper websites while fans exchanged their favourite quips from Discworld characters online.

This was one popular example:

"DON'T THINK OF IT AS DYING," said Death. "JUST THINK OF IT AS LEAVING EARLY TO AVOID THE RUSH."