I find the atheist to be the largest proponents of determinism. Most religions Embrace some idea of a soul, free will, and agency.

On the other hand, almost every atheist I know believes in some form of material determinism. For them, individual Behavior is entirely driven by the physical makeup of an individual and their interacting environment. They deposited if you had a sufficiently accurate model of the universe you would be able to determine every action they would make.