The Doctor
In G.I. Joe: The Rise of Cobra, he appears as the Doctor, a masked scientist helping James McCullen build a nanobot army. At the Arctic base, Duke learns who he is: Rex Lewis, the Baroness's brother, presumed dead in an airstrike during a mission Duke led.
Disfigured by the blast, Rex found Doctor Mindbender's nanobot research and implanted the machines in his sister, turning her into the Baroness under his control. As the base is destroyed, he takes the name Cobra Commander, uses nanobots to heal McCullen's burned face and puts him under his control. The Joes capture them both. His mask was redesigned because the comics version looked too much like a Ku Klux Klan hood.