5. Dr. Joseph Mengele
Also known as the Angel of Death, Joseph Mengele gained notoriety mainly for being among those who supervised arriving prisoners. He would get to determine who was fit to become a forced laborer and who would be killed.
He would also perform human experiments on camp inmates. Mengele performed twin studies at Auschwitz where he would then kill the twins and dissect their bodies after the experiment was over.
He is also said to have sewn two children together to create conjoined twins. All his operations including those of the heart were done with no anesthesia.