The Stanford prison experiment, perhaps the most well-known of any mentioned here, was conducted in 1971 by Philip Zimbardo with an aim to study what psychological effects are entailed in becoming either a prisoner or a prison guard. Here 24 male subjects were taken and randomly selected to be either guards or prisoners within a mock prison in the basement of the Stanford psychology building.
Zimbardo was reportedly impressed at how quickly the subjects adapted to their roles, as the guards quickly took on more and more authoritarian roles and eventually even resorted to the psychological torture of the prisoners. Not only did the prisoners take the psychological abuse passively, they even went so far as to harass other prisoners at the requests of the guards. It was not until after Zimbardo himself started to condone the abuse that two prisoners quit the experiment early and it was all stopped after only six days.