Patrick Jane from THE MENTALIST fits the description of an athiest to a tee. His wife and daughter were murdered and he will mock religious beliefs or any belief in the supernatural, although he may have been an atheist before since he was a secretly fake psychic before the murders. In fact, this is what got his family killed after he did a fake "reading" of a serial killer, so it explains his hostility to such beliefs.
In HOUSE M.D. the title character is an utterly cynical curmudgeon, Straw Nihilist atheist as well as a bitter drug addict. Dr. House is actually a more benevolent example than most. In a few more reflective moments, he explains that in the absence of definitive proof one way or another, a belief for or against God is ultimately a choice between what gives more comfort. He simply finds it more comforting to think that existence isn't a test.
All through the INDIANA JONES franchise, Indy found strong evidence of a number of religions. Yes, the Holy Grail was evidence in favor of Christianity. The Sankara stones support Hinduism. And the Ark of the Covenant supports Judaism. And it’s that multiplicity of evidence that would likely make him sorta-kinda sn athiest. But it wouldn’t be athiest in the “I don’t know if there are any gods” kind of way, but rather in a “there are definitely greater powers, but I don’t understand any of it” way. Notably, the Grail and the Sankara stones support conflicting narratives. The Grail supports Christianity and therefore a monotheistic universe. The Sankara stones, associated with different gods, support a polytheistic universe. The Ark…well, Judaism doesn’t have just one approach to other people’s gods, so there are a few different ways THAT could go!