Science fiction pioneer Philip Jose Farmer "passed away peacefully in his sleep," his website noted this morning.

The 91-year-old author was best-known for his Riverworld series, a surreal collection of books about a world where historical figures mingle on a watery planet. Wikipedia counts six Hugo Award nominations for the author during his long career.

Here's more from the PJ Star: He was once quoted as saying that, particular in his early career, he had more fans in France, Italy, Germany and Japan than in the United States. Even after he retired from writing, his fans continued to produce 'Farmerphile,' a magazine devoted to his life and works." (Via Scalzi)