It is generally accepted that the more books a contemporary author sells the less well-received the books are by the critics.

If that is true then Terry Pratchett, whose Discworld novels sit on the bedroom shelves of millions of teenagers, must be despised by the literary community.

Certainly, despite the fact he has been a literary phenomenon since the 1980s, critics have always raised a sneering eyebrow when it comes to his output.

One in every 100 books published in the UK bears his name and worldwide he has sold 27 million copies of his books.

He also has the dubious distinction of being Britain's most shop-lifted author.

Boast

In the UK, JK Rowling and Jeffrey Archer cannot beat the Beaconsfield-born writer who can boast 12 of his books on the top 5,000 best seller lists for the last 300 weeks.

In 19 years he has written 47 books, including six books for small children and a graphic novel.

Pratchett has sold 27 million books

If his success is built on anything, it is a great turtle, supporting four giant elephants, holding up Discworld, the giant creation of his imagination.

Discworld is the crucible of his mind, a fantasy land which has produced 28 novels, all of which can be read independently, yet together they create a rich world of ideas, characters and stories.

"Fantasy allows you to reflect things happening in our world by looking at it in a slightly distorting mirror," the author told the BBC in an interview.

"You can see and comment on humanity from an outsider's perspective."

Parody

The Colour of Magic was his first successful novel, published in 1983 but his writing career had begun 15 years earlier with the novel, The Carpet People.

But he was always a writer - his first short story was published when he was just 13-years-old, in a school magazine.

His work was condemned by the headmaster as "morally suspect" which sent sales of the publication through the roof.

The studio behind Shrek is adapting a Pratchett trilogy

His writing, followed up by two science fiction novels, was characterised by parody and it was not until he learnt how to both make fun of the fantasy genre and revere it before he found success.

Side-splitting comedy - designed to make readers embarrass themselves in public - has always been the trademark of his books.

The Discworld novels have become essential readings for many teenagers whose imaginations are awakened by his rich writings.

If the critics have not taken note, Hollywood has. The studio behind Shrek is in pre-production on a film version of his trilogy, called The Bromeliad.

His worlds are patrolled by wizards, trolls, heroes and villains but they possess the kinds of human frailties not often depicted in the standard hack and slash fantasy books.

Enjoy reading

Pratchett was born in 1948 and has said the family home did not have any electricity and there was just a tin bath.

He did not enjoy reading until he was 10 years old, and the first book to resonate with him was The Wind in the Willows.

At 17 years old he became a newspaper reporter on the Buckinghamshire Free Press.

There may not be much connection between his original career and his later writings, but he has said he feels some of the bad press he gets is down to journalists hating to hear about their colleagues' success.

Grown-up

He may not be familiar to readers of the London Review of Books but he is easily recognisable in his trademark black clothes and hat.

He looks like, and probably is, a grown-up version of the young people who read his books.

But his audience has grown over the years and not just in number.

His readers have grown up with him and many adults can now be counted among the faithful.

As Pratchett himself has said: "I can't walk into a bookshop and spot my readers any more."