The atheist also has a God, and it is himself.
The idolater at least understands that there is something above him, something beyond the grasp of his physical senses, external forces to which he is subject.
But for the atheist, the entire universe is defined by his own understanding, all ethics are subject to his approval, and even he himself is a construct of his own mind. He is a self-made man, because he creates his own universe and inserts himself into it.