Who are the Combine Overwatch? "The Combine Overwatch is the transhuman military branch of the Combine's Occupation on Earth, following the Seven Hour War. After disbanding the US Armed Forces and many other international militaries, the Combine replaced their main synth war foot-soldiers with surgically augmented humans, artificially programed to kill Xen wildlife and normal humans. They also support and protect vital Combine resources, nexuses, and synths from the Resistance."
Picture credit to TheParryGod