Kyros is an ancient Greek and one of the first Dark-Hunters ever created. He was friends with Alexion when they were both human.
Stryker fed Kyros lies about Acheron to make him go rogue and turn against the Dark-Hunter cause. Kyros recruited Marco, Tyrell, and Squid, but he failed to recruit Danger, Rafael, and Ephani. In the end, however, he realized the truth and switched back to the right side.