Karl Hass (5 October 1912 – 21 April 2004) was an SS Sturmbannführer and German spy who helped deport more than 1,000 Italian Jews to Auschwitz. A perpetrator in the Ardeatine massacre, in which 335 civilians were murdered, he was tried and convicted in Italy in 1998. Hass subsequently spent the remainder of his life under limited house arrest.
Hass had Princess Mafalda of Savoy, the daughter of King Vittorio Emanuele III of Italy, placed into German military custody, which eventually resulted in her death. He reputedly lured her to his headquarters in Rome by the suggestion that there was a message from her husband, who was then being held in Berlin. On her arrival at the German command, Hass had the princess arrested and sent for questioning to Munich. She was subsequently sent to Berlin and then to the Buchenwald concentration camp, where she was wounded in an Allied bombing raid. Despite receiving medical attention at the camp, she died following an operation to amputate her infected arm. Only Kappler was charged with the Ardeatine cave massacre.
At some point in the 1960s, Hass returned to Italy. According to journalist Mario Tedeschini Lalli, Hass appeared as an extra in several Italian films, including Luchino Visconti's The Damned and Massacre in Rome - a film about the Ardeatine massacre. He may have also been employed by filmmakers as a technical advisor.