Actually, I believe his birth name was William Motherfucker, but he had to change it when he went into showbiz, as with so many actors before him.
Reminds me of that awful old joke about unsuccessful actor Penis von Lesbian, who couldn't get a gig, refused to change his name, and was subsequently dropped by his agent. Years later they ran into each other and the latter was surprised at what he saw- the former rolling in dough.
When asked how he attained such success, Penis replied, "Oh it was easy! All I had to do was finally agree to change my name."
"What in the world did you change it to?" asked the agent. "How did you achieve such fame and fortune?"
"Oh, nothing fancy. Just Dick van Dyke."