Who is the man in this picture?

In the texture files of the video game Half-Life, there are black & white pictures of (moderately) famous American men. They include Martin Luther King, Malcolm X, Babe Ruth and Thurgwood Marshall. There is one I cannot identify. He might be some scientist, of someone from Seattle (where the game developers hail from), a writer, or something else. Here's the (tiny) pic: http://img508.imageshack.us/img508/1486/picture10m.png