Unlike strict monotheistic systems, we are polytheists, and also believe that a "mortal" being with a conscious soul can achieve Godhead, becoming immortal and Divine.
Some Daemons and great Humans of history are now immortal and have been seen as Gods and called Gods.
But there are Gods that are more "typical" in the sense that they have always existed. I do not know exactly which Gods this applies to, and I'd rather not speak in ignorance, but I am definitely certain this applies to Zeus.
Zeus is not "just" a God, he is GOD. He is the Uncaused Causer, the Unmoved Mover, the Divine Mind in which Existence was conceived, the primordial First Soul to gain self-knowledge (Adi Guru), the first ever source of all Energies (Adi Shakti). He is Being itself, and also beyond Being.