To quote Locus Online:
"SF Grand Master Jack Williamson, born 1908, died this afternoon at his home in Portales, New Mexico, at the age of 98."
He was an amazing man. First published story in 1928, at age 20; last published novel in 2005, at age 97 or so. In between, he wrote over forty novels and over a hundred short stories.
He received the Nebula Grand Master award in 1975, in his late 60s, and then he kept writing for another thirty years. He received a World Fantasy Award for Life Achievement in 1994 and a Bram Stoker Award for Life Achievement in 1998, and then he kept writing for another nearly ten years. He won his first and only Hugo and Nebula for a specific work of fiction in 2001, both for his novella "The Ultimate Earth," at age 94.
His impact on the field was impressive. According to Wikipedia, "[h]is Legion of Time (1938) was the first story to feature alternative future civilizations sending agents back to the present day, to fight over actions that will decide their future existence"; that article also mentions that he coined the word "terraforming." And: "By the 1930s [Williamson] was an established genre author, and the teenaged Isaac Asimov was thrilled to receive a postcard from Williamson, whom he had idolized, congratulating him on his first published story and saying "welcome to the ranks."
He was among the first to use the term "genetic engineering," and among the first to write fiction about in vitro insemination, space habitats, organ banks, and antimatter. (According to a Science Fiction Weekly interview from a couple of years ago.)
Oh, yeah, and Williamson had a Ph.D. in English Lit; his thesis was on H. G. Wells.
I'm sad to see him go.
I haven't seen any obits yet, but I'm sure they'll start appearing soon.