Stanley Milgram
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.