McGill is a double-agent sent by Project Cadmus into the D.E.O. to annihilate aliens.
Biography
After Supergirl brought Superman to the D.E.O., McGill shook his hand and admitted that it was an honour to meet him.[1]
After Alex and Winn deduce that McGill is the one who has been stealing kryptonite from the DEO supply, Alex told him that they are preparing a new shipment of the mineral and she wants him to lead it. She followed and cornered him when he tried to smuggle the kryptonite away from the transport. However, before Alex could interrogate him, he was shot by two agents from Cadmus.[2]