Kurt Vonnegut's son has hit out at a new biography of the Slaughterhouse-Five author which paints him as a bitter, lonely old man.

Charles Shields' And So It Goes depicts Vonnegut as an angry man prone to fits of depression, cruel to his first wife and even investing in Dow Chemical, a maker of napalm. Vonnegut was desperate for appreciation, Shields writes, describing a meeting with the author a few months before his death in 2007 when Vonnegut's own name was not to be found in a dictionary, but Jack Kerouac's was. Frowning, Vonnegut then asked: "How about that?"

"Kurt was not the person I expected to meet," Shields told the Charlottesville Daily Progress in an interview in which he describes the author as a friend. "He struck me as a man who was in pain and who was haunted by the past. When you read his books you get his droll sense of humour and his joshing. You get his kind of avuncular attitude. Then, when I meet him, I find an 84-year-old man who is angry about his parents, and is unhappy about his first marriage that ended years before. He feels he is unappreciated by critics, that he has been ignored by the eggheads. So I met a man who should be enjoying the golden years of fame and success. Instead he comes off as a very aggrieved person who wanted to settle some scores, and wanted it known just how he had been treated."

But Mark Vonnegut, the late author's son, has disputed the portrait of his father drawn by Shields. "I'm happy to reassure you that Kurt did not die a bitter man who kept thinking he was a failure," he has written in an email to the science fiction website io9.

Vonnegut did not, said his son, buy Dow stock, and had "next to no interest in investments or expensive things", claiming that Shields had ignored a lot of evidence in order to produce his portrait of the writer.

The biographer, writes Vonnegut's son, "spent very little time with a much diminished 84-year-old who right up to the end showed more flashes of brilliance and warmth than most. There's a ton of evidence, including his art and writing, that he fought hard and largely succeeded to overcome PTSD from WWII and a quirky, but not altogether unloving childhood to have mostly loving and supportive relationships with his siblings and children and even his allegedly distant father".

Although Vonnegut's son admits that the acclaimed science fiction author was "not a perfect man or father, and I'll grant you two failed marriages", he ends by calling on readers to "employ a modicum of critical thinking before buying into the truth of a book whose existence is completely and utterly dependent on a picture that Shields would have made up out of whole cloth if he had to".