The man who wrote under the name "William Tenn" was Philip Klass, and he has died at the age of 89.
I had the great honor of shaking Mr. Klass's hand at the 2004 World Science Fiction Convention in Boston, the only WorldCon I have (so far) attended. He was the Guest of Honor, and I somehow ended up at the Hugo Losers Party, and he was there to hang out with the losers. He seemed quite happy to be in such company.
Shaking his hand was, for me, one of those awkward moments where English suddenly seemed to stop being my native language. All I could manage to say was, "I really admire your work," and he smiled and nodded. I must have been about the five hundredth person that day to say such a thing to him, and probably some of the people who said such a thing to him didn't even know who he was. I wanted him to know that I knew, that I thought everyone should know the name of the man who wrote "The Liberation of Earth", a story I cherish. But I couldn't find the words, and so I smiled and nodded, and he smiled and nodded, and then I fled.
He wrote "The Liberation of Earth" and "Down Among the Dead Men" and "Brooklyn Project" and "The Custodian" and plenty of others. They are currently most easily available in the three volumes of collected fiction and nonfiction published by NESFA Press: Immodest Proposals, Here Comes Civilization, and Dancing Naked.
In 2004, I wrote a long post about the short stories in general and "Liberation of Earth" in particular.
The official William Tenn website has a running list of links to remembrances and appreciations.
Words seem, once again, to be failing me, and so I will, once again, offer Phil Klass and William Tenn a smile and a nod -- this time in honor of his memory and in thanks for the stories he gave to the world.