Clockwerk

Clockwerk (stylized as CLOCKWЯK) was a Eurasian eagle owl that was the leader of the Fiendish Five and nemesis of the Cooper Clan. He was consumed by jealousy for the Cooper Clan's reputation as thieves and hated them to such a degree that he replaced his mortal body with soulless machinery just to keep up with them through time. He was eventually killed by Sly Cooper, though his legacy continues to haunt the Cooper Gang to the present day.

Clockwerk is considered by many to be the main villain of the Sly Cooper series, and is the only villain to be referenced in all four games.