Who came up with the theory of six degrees of separation?

Thought this was cool…. even more prevalent in the deaf world, which is like 1% of the entire population.

Yahoo! Answers – theory of six degrees of separation

In 1967, psychologist Stanley Milgram tried to test the theory by sending several letters to random people in the Midwest. The letter featured the name, address, and occupation of a single person on the East Coast; participants were asked to forward the letters to the people who they thought were most likely to know the person. It took an average of five intermediaries to reach the target.