Like Mark Twain, Mr. Vonnegut used humor to tackle the basic questions of human existence: Why are we in this world? Is there a presiding figure to make sense of all this, a god who in the end, despite making people suffer, wishes them well?

He also shared with Twain a profound pessimism. “Mark Twain,” Mr. Vonnegut wrote in his 1991 book, “Fates Worse Than Death: An Autobiographical Collage,” “finally stopped laughing at his own agony and that of those around him. He denounced life on this planet as a crock. He died.”