Zyklon

Zyklon was a supernatural villain from Marvel comics, the empowered spirit of the real-world Heinrich Himmler he was risen from the dead as an agent of Satannish alongside several other historical villains and granted demonic powers based on what he was famous for in life: namely the execution-chambers, making him in many ways a walking gas-chamber.

He was part of the Lethal Legion (somewhat ironically fighting next to Coldsteel, despite them being bitter enemies in real-life) and fought against the Avengers West Coast before being defeated and was returned to his place in Mephisto's hell dimension.

His name is a reference to Zyklon B - a gas used by the Nazis to kill thousands during the (very real) Holocaust.