Unmensch a was a cyborg Nazi in the service of Ilsa Haupstein. "Unmensch" is German: "Mensch" = "human"; "un-" is a prefix use to negate somthing, "Unmensch" can mean both: something not human or a human who acts sadistically (the more common meaning) - today the term is used very often denoting Nazis in Germany.
Wake the Devil
When Hellboy crashes through the roof of Haupstein's castle, Unmensch is ordered to attack him. Hellboy is hit several times with Unmensch's powerful mechanical arm, before the two go crashing through the floor, where Unmensch disappears. However, Hellboy does managed to discover the mechanichal monster's detatched arm, and later, his severed head.
Abilities
Similar to Mr.Winks, Unmensch's mechanical arm can extend due to a chain linking to his fist. Unmensch has enhanced strength.