A new biography of acclaimed American author Kurt Vonnegut, beloved by fans worldwide for his work's warm humour and homespun Midwestern wisdom, has shocked many with a portrayal of a bitter, angry man prone to depression and fits of temper.

The book on Vonnegut, who died in 2007, lifts the lid on the writer's private life, revealing a man far removed from the grandfather-like public figure his millions of devotees adored.

And So It Goes was written by Charles Shields, who also wrote a controversial biography of Harper Lee, author of To Kill A Mockingbird. The book paints a picture of a man who was often distant from his children, cruel to a long-suffering first wife, caught in an unpleasant second marriage and spent much of his later years depressed and angry. "Cruel, nasty and scary are the adjectives commonly used to describe him by the friends, colleagues, and relatives Shields quotes," wrote one reviewer, Wendy Smith, on the Daily Beast website. The New York Times reviewer, Chris Buckley, called Shields's portrayal "sad, often heartbreaking".

Through novels such as The Sirens of Titan, Cat's Cradle and the classic Slaughterhouse-Five, Vonnegut's career spanned five decades, often working in the science fiction genre, and catapulted him into the canon of great American writers. His work, while often dealing with tragedy, was famed for espousing humanitarian, even socialist values, and often had a strong anti-war, anti-capitalist feel. It is full of references to the virtues of small-town life, volunteer firefighters and the Midwest, especially his home city of Indianapolis.

Yet Shields's book is unsparing in its portrayal of Vonnegut's dark side. It reveals that the writer – whose experience as a PoW during the firebombing of Dresden scarred his psyche for life – had no qualms about investing in firms that made napalm or indulged in a host of other morally suspect activities. He fell out with friends, editors and relatives and had a shocking temper. In later life he appeared deeply bitter and lonely. In the opening part of the book Shields describes meeting Vonnegut just a few months before his death. He describes Vonnegut asking him to look up his name in a dictionary (it was not there) and then look up Jack Kerouac (it was there). "How about that?" Vonnegut then states with a frown. The chapter of Shields's book dealing with Vonnegut's final 15 years of life is called simply "Waiting to Die".

"Towards the end he was very feeble, very depressed and almost morose. I think that slants this book," said Jerome Klinkowitz, an academic at the University of Northern Iowa and one of the world's leading experts on Vonnegut.

"It is a little naive to be surprised by this," said Gregory Sumner of the University of Detroit Mercy, who recently wrote a book exploring Vonnegut's work, called Unstuck In Time. "Personal relationships were difficult for him. He had a lot of survivor's guilt."

Vonnegut definitely had survived a lot. His once wealthy family was impoverished by the Great Depression, causing grim strains in his parents' marriage. His mother committed suicide. His beloved sister died of breast cancer, a day after her husband was killed in a train accident. But the defining horror of Vonnegut's life was his wartime experience and surviving the Dresden bombing, only to be sent into the ruins as prison labour in order to collect and burn the corpses. The ordeal cropped up continually in his work, but most notably formed the basis of Slaughterhouse-Five, the book that made Vonnegut famous.

But there was more to it than just coping with such traumatic situations. In later life, despite being hailed by so many as an American genius, Vonnegut felt that the literary establishment never took him seriously. They interpreted his simplistic style, love of science fiction and Midwestern values as being beneath serious study.

The book will do little to dampen enthusiasm for Vonnegut's work. "He's not a relic of the 1960s. His work is vibrant today even posthumously," said Sumner. "Maybe we just expect too much of our heroes."