1. We use "the" in this situation to emphasise the fact that we're talking about a well-known person, so "the" is itself strongly emphasised (and for that reason pronounced "thee", as you say):
"My name is Bond. James Bond."
"Not the James Bond, surely?"
"Er... well no, James Bond is a fictional character and I just happen to have that name."
"I spoke with Robbie Williams yesterday."
"Yeah, nice guy, lives at number 29..."
"No, not him. I mean the Robbie Williams."
"Yes. I asked him for his autograph."
It follows then that we don't use the definite article when referring to somebody who is not well-known.
2. The indefinite article is pronounced quite normally.
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