Who is the all-time most known (ethnic) Pole?

[Incal]

Nationality and ethnicity are not the same thing.

Depends. In some countries they are, take for example asian nations like Japan, where a japanese national is also ethnic japanese for example.

In Europe it's not the case anymore but there are some exceptions like Ireland, where I think an Irish national is still Irish ethnically.

[Regnera]

I'd say Marie Curie.