There isn’t a precise answer to the OP’s question because atheism isn’t an ideology or philosophy or science or anything like that. It’s just an absence of a particular belief, so while there are lots of famous people who were/are atheists, few of them are famous only for that in the way that Darwin is for evolution because there’s nothing really to explore, pioneer or develop about it as a per se assertion, except to argue against assertions in favor of theism.
Even Dawkins, who has kind of become the most well known advocate for arheism and public critic of religion, was already well-known as an evolutionary biologist before he became famous for The God Delusion.
I think O’Hair is probably the most synonomous with “atheism,” but she isn’t really the exemplar most atheists would want representing them.
Originally best known as a magician (illusionist), now better known as a debunker of woo-woo, but since 2003, also well-known as a full-throated atheist, James Randi.
Judging by the lack of clarity for most historical figures and the lack of popular appeal for most of the living nominees, It seems like the answer is a simple, “No. While there are some atheists that are well-known in their fields, there are no atheists that are widely known.”