Byline: SIMON GASKELL
The trilogy was written by 49-year-old former TV executive Erika Mitchell writing under the pseudonym EL James.
She lives near Ealing, London, with a husband of 20 years and two teenage sons.
Her stories were developed from a Twilight fan fiction originally titled Master of the Universe published episodically on websites under the pen name "Snowqueens Icedragon".
The posts featured characters named after Stephanie Meyer's characters in the successful Twilight series - Edward Cullen and Bella Swan.
After comments over the explicit sexual nature of the material, James removed it from fan fiction websites and moved it to her own website - FiftyShades.com - instead.
The reworked and extended version of Master of the Universe was split into a trilogy. The first, Fifty Shades of Grey, was released as an eBook and a print-on-demand paperback in May 2011 by The Writers' Coffee Shop - a virtual publisher based in Australia.
The book, largely set in Seattle, features the relationship between virgin college graduate Anastasia Steele and manipulative billionaire Christian Grey.
Steele is required by Grey to sign a contract allowing him complete control over her life and the book contains explicitly erotic scenes featuring elements of bondage, discipline, sadism and masochism (BDSM).
The second volume, Fifty Shades Darker, was released in September 2011.
The third, Fifty Shades Freed, followed in January 2012. The trio of books started selling hundreds of thousands of eBooks before it was picked up by publisher Random House and sold more than 15 million copies in the US and Canada.
On March 26, 2012, it was announced the film rights to Fifty Shades had been snapped up by Universal Pictures and Focus Features after a bidding war with Paramount, Warner Bros and Sony.
There has been long list of actors linked with the lead roles of Christian Grey and Anastasia Steele, with the likes of Ian Somerhalder and Ashley Benson expressing an interest.
Meanwhile it has also been reported Angelina Jolie is interested in directing the film.
The licence to the Fifty Shades series was picked up by Vintage Books, a subsidiary of Random House, for re-release in a new and revised edition in April 2012.
At the end of June, the first book in the series - Fifty Shades of Grey - became the fastest adult novel to sell one million copies in paperback, smashing previous record holder The Da Vinci Code by Dan Brown.
The book took just 11 weeks to pass the million marker ahead of The Da Vinci Code, which took 36 weeks to top one million.
Meanwhile, it also superseded JK Rowling's book of fairy stories The Tales of Beedle the Bard which sold 367,625 copies in one week in 2008 by virtue of topping 397, 889 copies in just one week.
Philip Stone, charts editor of book trade magazine The Bookseller, said: "Sales of the Fifty Shades series have been nothing short of phenomenal and records are tumbling."
The success of the trilogy has given rise to a number of spoofs.
Among them on Twitter are the popular accounts 50 Sheds of Grey and 50Shades ofAndyGray.
The former describes itself as "Erotica for the not-too-modern male" and among its posts include: "We each drop our keys into the bowl. Before long we'll be entering a world of forbidden delights. God, I love these shed-swapping parties. …