The void golem, other known as the Corrupted Golem, is a boss that appears to be under the control of Varyn and the void element.
It once was a friendly golem which protected Gaia's temple. Not it seems to have corrupted with a purple sword in its shoulder. The sword looks very similar to the sword Kyros wears in a fanart. Maybe Kyros got evil through Varyn and then corrupted the Golem?