Gary Sitterson (Richard Jenkins) is one of the technicians in the control room controlling everything in the cabin in the woods, along with Steve Hadley. He serves as one of the two secondary antagonists of the film.
He was portrayed by Richard Jenkins, who would go on to portray Eli Raphelson in White House Down.
He is experienced and skilled at his job. He was able to release a gas that changed Curt Vaughan's mind in order to split up the group. When the tunnel failed to collapse, he was able to get it working again and collapse it.
He was killed during the System Purge when Dana Polk accidentally stabbed him. His last words were "Kill him.".