What does "a" followed by people's name mean?

Question

The following are the sentences appearing in an American film "Charade". What does "a" before people's names mean? Thank you.

I have never seen a Rothschild before.
Is there a Mr. Lampert?
Is there a Mrs. Joshua?

Answer 1

I have never seen a Rothschild here=I have never seen a rich man here.
Since Rothschild here is not a name, but a symbol of Wealth.
A rich Man=A Rothschild

Answer 2

It's an indication of something singular.

"There is a member of the Ferguson family," can be stated as, "There is a Ferguson."

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