Vonnegut was most famous for his novel Slaughterhouse Five, the story of a man, circa post-WWII, traveling at random through time, re-living the events of his own life, including his death, multiple times. The hero knows he is time-traveling as he repeats the events of his life, but he can do nothing to change events, or choose when or where in his life he will travel, or stop his time traveling. Eventually he accepts his fate, adopting the philosophy of fatalism, and in doing so he acquires peace.
Recurring themes throughout Vonnegut's work are determinism, iconoclasm, humanism, and fatalism, revealing much about the author's own attitudes to the world, and to life and death. He was also a great literary experimenter. Vonnegut's plots are disjointed, and many of his characters are more thematic devices than characters. He also used metafiction, using sections of a novel to write about the novel, sometimes appearing as himself in the narrative. For example, in Breakfast of Champions, one of his bestsellers, we get the great humorous exchange:
"This is a very bad book you're writing," I said to myself.
"I know," I said.
This novel is also a sort of all-star novel, featuring many cameos by characters from several other of Vonnegut's works, including, for example, the frequently appearing Kilgore Trout, an unsuccessful though prolific sf writer.