Iusnaturalism

Iusnaturalism and the "Natural law" might seem as merely suppositions, or even as religious inventions by (St.) Thomas Aquina. He might be considered as the father of iusnaturalism, but what Thomas Aquina really did was an interpretation (and in some cases, reinterpretation) of Artistotle's work.

So, what might seem as something irrational, was originally developed by one of the world's most intelligent men ever. Yes, Aristotle believed in an universal law, although he never stated what was this universal law exactly.

http://en.wikipedia.org/wiki/Opium_of_the_People