John Stuart Mill
They say this fascinating thinker is one of the fathers of Utilitarianism, but might he not equally be considered a father of Libertarianism? This quote seems to embody the fundamental essence of such sentiment.
The only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others. His own good, either physical or moral, is not sufficient warrant.
I’m not sure, clearly, I’ll have to do some more reading, but this is a wonderful example of convergent independent thought if indeed Mill had no impact on Libertarianism.