Vonnegut, regarded by many critics as a key influence in shaping 20th-century American literature, died Wednesday at 84. He had suffered brain injuries after a recent fall at his Manhattan home, said his wife, photographer Jill Krementz.
In a statement, Norman Mailer hailed Vonnegut as "a marvelous writer with a style that remained undeniably and imperturbably his own. ... I would salute him — our own Mark Twain."
"He was sort of like nobody else," said fellow author Gore Vidal. "Kurt was never dull."
Gay Talese, a best-selling author who knew Vonnegut well, told CBS News correspondent Richard Schlesinger that he never heard Vonnegut "express a bit of vengeance, resentment ... although in his work there was that real keen sense of hypocrisy."
"He was not a mean man," Talese added. "And boy, that says something for writers."
Vonnegut's longtime friend and manager, Donald Farber, said there would be no public memorial, only a private gathering of family and friends. He also said other Vonnegut books were likely to come out, but declined to offer specifics.
A self-described religious skeptic and freethinking humanist, Vonnegut used protagonists such as Billy Pilgrim ("Slaughterhouse-Five") and Eliot Rosewater ("God Bless You, Mr. Rosewater") as transparent vehicles for his points of view.
He lectured regularly, exhorting audiences to think for themselves and delighting in barbed commentary against the institutions he felt were dehumanizing people.
"He was a man who combined a wicked sense of humor and sort of steady moral compass, who was always sort of looking at the big picture of the things that were most important," said Joel Bleifuss, editor of In These Times, a liberal magazine based in Chicago that featured Vonnegut articles.
Some of Vonnegut's books were banned and burned for alleged obscenity. He took on censorship as an active member of the PEN writers' aid group and the American Civil Liberties Union.
The American Humanist Association, which promotes individual freedom, rational thought and scientific skepticism, made him its honorary president.
Vonnegut said the villains in his books were never individuals, but culture, society and history, which he said were making a mess of the planet.
"I like to say that the 51st state is the state of denial," he told The Associated Press in 2005. "It's as though a huge comet were heading for us and nobody wants to talk about it. We're just about to run out of petroleum and there's nothing to replace it."
Despite his commercial success, Vonnegut battled depression throughout his life, and in 1984, he attempted suicide with pills and alcohol, joking later about how he botched the job.
"I will say anything to be funny, often in the most horrible situations," Vonnegut, whose watery, heavy-lidded eyes and unruly hair made him seem to be in existential pain, once told a gathering of psychiatrists.