My favourite illustrative example of definite vs. indefinite articles

[maradydd]

"You are Zaphod Beeblebrox?" it squeaked.

"Yeah," said Zaphod, "but don't shout it out or they'll all want one."

"The Zaphod Beeblebrox?"

"No, just a Zaphod Beeblebrox, didn't you hear I come in six-packs?"

--Douglas Adams, The Restaurant at the End of the Universe