Harry Potter creator JK Rowling has been unmasked as the crime author Robert Galbraith. Using a pseudonym is a common trick among authors who want to hide their identity, swap genres or just get a better spot in the book shop.

Rowling joins the likes of the Bronte sisters, Doris Lessing and Ruth Rendell on the list of authors who have adopted noms de plume.

"I can absolutely understand why JK used a pseudonym," says literary agent Jane Gregory, who co-founded the Harrogate Crime Writing Festival and the Orange Prize. "The knives were out for her, weren't they?"

Rowling invented Robert Galbraith as a pen name to publish The Cuckoo's Calling without the hype and expectation that came with being JK Rowling.

And it was met with enthusiastic reviews, if modest sales.

"When she wrote The Casual Vacancy [her first post-Harry Potter book], they were all waiting desperately to attack it," Ms Gregory continues. "And this time actually the reviews across the board are fabulous."

Image caption The Robert Galbraith novel follows a private detective with a wooden leg

EL James must be watching with interest. The 50 Shades author recently said she would write her next book under another name. Critics and readers will now be desperately trying to spot it.

There is a long history of authors changing their names. In 1984, Doris Lessing said she wanted to escape "from the cage of my literary reputation" when she began writing under the pen name Jane Somers.

She did not reveal Somers's true identity to her British publisher, who rejected the manuscript. The book did find a publisher, but sold only 2,000 hardback copies.

Other authors have different reasons to obscure their identities. Charlotte, Emily and Anne Bronte initially named themselves Currer, Ellis and Acton Bell.

Their gender was deliberately ambiguous because, Charlotte later said, they knew that "authoresses are liable to be looked on with prejudice".

Have times changed? JK Rowling's publisher changed her name on the first Harry Potter book cover from Joanne to JK because they believed that girls did not care who had written a book, but boys would not buy a book by a woman.

For some writers, a new name can create a new persona and open the door to a new genre.

Booker Prize winner John Banville writes detective novels under the name Benjamin Black. He has said he can craft 100 words per day as Banville, but can rattle out a couple of thousand as Black.

If you were writing a book you really wanted females to read, I would go for initials. You want things that are powerful and that people won't forget Jane Gregory, Literary agent

When not writing murder mysteries, Ruth Rendell writes under an alter ego, Barbara Vine, whose works she describes as more "serious, searching, analytical".

Other choices come down to cold hard business.

Jonathan Freedland, a Guardian columnist who writes thrillers under the pseudonym Sam Bourne, says: "The name Jonathan Freedland just doesn't sound like a thriller writer's name, whereas Sam Bourne does.

"The publishing experts said the trouble with Jonathan Freedland was that it had too many syllables. It's too long. It's better to be higher up in the alphabet. There are all these commercial considerations.

"But also the idea is a separation from the day job, just to keep the two distinct, in readers' minds but also in your own mind."

When Tania Carver's debut thriller, The Surrogate, was nominated for the 2010 Theakstons Crime Novel of the Year Award, the author was invited to appear at the award ceremony at the Harrogate Crime Writing Festival.

Except when Carver's name was read out, Martyn Waites walked to the podium. There is no Tania Carver - it turned out to be a pseudonym for Waites, already an established crime writer, and his wife Linda.

Shelf space

Tania Carver was born when Waites' editor mentioned a gap in the market for a high-end female thriller writer, a British answer to Karin Slaughter.

Waites thought he could fill that niche. Initially sceptical, his editor liked the results and went about choosing a name.

The editor wanted a surname beginning with C, Waites says, because shoppers' eyes are naturally drawn to the top of the second bookshelf in a book shop. That is normally where books by "C" authors live.

"When I was writing as Martyn Waites, I was right at the end. People had to bend down to the bookshelf and get them," he laughs. "They wouldn't bother and they'd get Lee Child instead."

The name Tania Carver also has the same crime connotations as Karin Slaughter, and trips off the tongue in the same way. "And I've got to say it worked," Waites says. (Karin Slaughter got lucky - that is her real name.)

Make it memorable

So, how do you go about choosing a pseudonym? I ask Jane Gregory for advice on choosing an alternative to Ian Youngs for my (non-existent) debut crime novel.

"I would certainly drop the 's'," she advises. "People would forget it.

"It would depend on the kind of book you are writing. You'd then pick a name that would be right within that genre. If you were writing a book you really wanted females to read, I would go for initials. You want things that are powerful and that people won't forget.

"People keep saying that you don't want to be 'A' [for a surname] because you don't want to be too far up the shelf, and you don't want to be 'Y' because you're in the bottom right hand corner. You want to be in the busy middle."

I take my forename initials - I.S - and try to think of a memorable surname high up the alphabet that has not yet been taken. I settle on IS Cleaver.

Could it be a best-seller? I doubt it. And I suspect there is much more to literary success than a name.