Stanley Milgram

You might not know the name, but you know this man's work. Social psychologist Stanley Milgram conducted an experiment in the early sixties in which perfectly "normal" Americans were instructed to administer electric shocks to strangers sitting in another room. Of course, there was no actual voltage, but what Milgram's disturbing findings yielded was that 65 percent of the people involved in the experiment were willing to apply the maximum voltage possible to their unknown, unseen counterparts simply by being instructed to. Conducted in the smug enlightenment of Yale, the "Milgram experiments" had damning ramifications for everyone, coming on the heels of the Eichmann trial, the initial furor over Arendt's "banality of evil" theory, (which of course Milgram validated) and foreshadowing how far "average" Americans would cave in to the dark side in the nascent Vietnam war.
This experiment is legendary, but what most people remain unaware of is Milgram's other work. He was largely responsible for popularizing the "six degrees of separation" concept through his "small world" experiments. In these, Milgram randomly decided upon the cities of Wichita, Omaha, and Boston, with the goal of seeing how closely associated people are who don't personally know each other. He mailed packets to individuals in Omaha and Wichita containing details of the project's purpose and then an address of another random individual living in Boston. The receiver of the package was asked if he or she knew the person in Boston whose address was in question, and if not, to forward the package to a friend or relative who might. Once the package finally reached the target address in Boston, Milgram could calculate the number of acquaintances that removed the two subjects. At the end of the experiment, the average stood at 5.5 or 6, thus solidifying, at least in the popular unconscious, the notion of "six degrees of separation" between everyone in the world.
Milgram is a personal hero of mine; his detached humanism has a lot of humor to it, a lot of bite, and very lasting implications.