Josef Mengele was an infamous physician working for the Nazi regime during the Holocaust, where he became in many ways a real-life version of a mad scientist - conducting terrible experiments on prisoners that earned him the nickname of the "Angel of Death": some of Mengele's victims were children, further adding to his infamy.
Mengele's experimentation was part of a wider network of such atrocities that were committed by so-called "doctors" and "scientists" during this time, taking advantage of the Holocaust to further their own unethical projects.
Mengel died in 1979 - aged 67, having managed to evade numerous manhunts performed after WWII to try and capture former Nazis (especially those involved in the Holocaust).