Stanley Milgram (August 15, 1933 – December 20, 1984) was an American social psychologist. He is most famous for his controversial study about obedience to authority figures. He got the idea from the Holocaust. He wrote a book about it called Obedience to Authority.
The idea of six degrees of separation comes from Milgram's 1967 small-world experiment. It has been criticized a lot, but in 2008 Microsoft found that the average chain of contacts between users of its '.NET Messenger Service' was 6.6 people. A study published in the January 2014 volume of Computers in Human Behavior found that the average number of acquaintances separating people in unusual jobs is 3.9, and 3.2 for average Facebook users.