The book, a mystery novel, had been published under the name Robert Galbraith.
On the website of the book's publisher, Robert Galbraith is described:
Robert Galbraith is married with two sons. After several years with the Royal Military Police, he was attached to the SIB (Special Investigation Branch), the plain-clothes branch of the RMP. He left the military in 2003 and has been working since then in the civilian security industry. The idea for protagonist Cormoran Strike grew directly out of his own experiences and those of his military friends who have returned to the civilian world. Robert Galbraith is a pseudonym.
Anyway, the most impressive part of it all is how widely liked the book seems to have been.
Here's a smattering of reviews from Goodreads.com:
And here are some snippets from Amazon's roundup of reviews:
"Instantly absorbing, featuring a detective facing crumbling circumstances with resolve instead of clichéd self-destruction and a lovable sidekick with contagious enthusiasm for detection. Strike bears little resemblance to Jackson Brodie, but Kate Atkinson's fans will appreciate his reliance on deduction and observation along with Galbraith's skilled storytelling." (Booklist)
"Plenty of twists...Totally engrossing...Galbraith's take on contemporary celebrity obsession makes for a grand beach read." (Library Journal, starred review (Mystery Debut of the Month))
"THE CUCKOO'S CALLING reminds me why I fell in love with crime fiction in the first place." (Val McDermid, bestselling author of The Vanishing Point)
"Cormoran Strike is an amazing creation and I can't wait for his next outing. Strike is so instantly compelling that it's hard to believe this is a debut novel. I hope there are plenty more Cormoran Strike adventures to come. A beautifully written debut novel introducing one of the most unique and compelling detectives I've come across in years." (Mark Billingham, author of The Demands)
"Robert Galbraith's debut is as hardbitten and hard-driving as its battered hero. CUCKOO'S CALLING scales the glittering heights of society even as it plumbs the dark depths of the human heart. A riveting read from an author to watch." (Mike Cooper, Shamus Award-winning author of Clawback)
This is quite an accomplishment. Starting over. Going with a new name, and then being beloved by readers all over again.
Only in literature is it concievable to pull off something like this... hats off to Rowling for doing so.