The Fiddler (Captain America)
Nazi saboteur undercover as a violinist who appeared in the "Horror Plays the Scales" story of Captain America Comics #7 (October, 1941). Real name Ulrich Kuster. He's part of an overly-complicated plot to assassinate anti-Nazi Senators by setting off explosives hidden in their radios with certain frequencies played in the Fiddler's radio show. Seems like it would just be easier to shoot them.
The Fiddler can also hit certain notes that kill people yet somehow the Fiddler is unaffected.