Where does “Αθανάσιος” come from?

Αθανάσιος (Greek) comes from Ancient Greek ἀθανάσιος, from Ancient Greek ἀθάνατος, from Ancient Greek ἀ-, from Proto-Hellenic hə-, from Proto-Indo-European sm̥-, from Proto-Indo-European sem- — together, one.

Αθανάσιος (Greek): Athanasius; given name Athanasios