It's important to note that this is a direct transliteration of the English name, not a true Greek name. There are no common Greek names that are direct equivalents of William.
However, if you are looking for a Greek name that has a similar meaning or feel to William, you could consider:
* Βασίλειος (Vasileios) meaning "king" or "royal"
* Γουλιέλμος (Goulielmos) another transliteration of William, but more common in historical contexts.
* Βίκτωρ (Viktor) meaning "victorious" or "conqueror"