But he is also not the son of Kirk Douglas.
Insane fake-name connections: http://www.cracked.com/article_18613_6-insane-true-stories-behind-stage-names-celebrities_p2.html
cliffs: Michael "Keaton" was actually born Michael Douglas, but due to existing names in the entertainment industry, he changed it to Michael Keaton -- because he thought Diane Keaton's name sounded cool. But Diane Keaton's real name is actually Diane Hall (the last name of which Woody Allen intentially referenced in the title of the movie Annie Hall). And most likely Diane changed her name out of admiration for Buster Keaton -- whose real name is Joseph Keaton, but who allegedly earned the nickname "buster" by Harry *Houdini* -- of course, also a stage name.