Douglas Adams (1952-2001) was a famous author, scriptwriter and humorist. He is best known for the "The Hitchhikers' Guide to the Galaxy", a must-read not only for nerds and geeks ;-) The story was originated as a radio comedy back in 1978 but then was released as a "trilogy" of five books that sold more than 15 million copies.
How can I celebrate?
If you haven't read the Hichhikers' Guide - today is the day to do it. If you know it... just read it one more time. In any other case... just think about the meaning of life, the universe and everything (spoiler alarm - it's 42).