Though never exactly a part of the science fiction community, Vonnegut used science fiction heavily in his works, many of which were humanist morality tales. He is probably best known for Slaughterhouse-Five and Galapagos. The latter earned him an honorary anthropology degree and demonstrated he had a better understanding of evolutionary theory than some scientists.
I will probably remember him most as the creator of the character Kilgore Trout, a fictional sleazy sf writer. One of Trout's novels, Venus on the Half-Shell, actually saw print as a hoax. Famed sf author Philip Jose Farmer, best known for Riverworld, eventually admitted to being the author. Apparently it took some wheedling to get Vonnegut's permission to write it.
Here's the article on Vonnegut from The New York Times:
Kurt Vonnegut, whose dark comic talent and urgent moral vision in novels like “Slaughterhouse-Five,” “Cat’s Cradle” and “God Bless You, Mr. Rosewater” caught the temper of his times and the imagination of a generation, died Wednesday night in Manhattan. He was 84 and had homes in Manhattan and in Sagaponack on Long Island. [more...]