It goes back to the ancient Greek goddess of wisdom, Athena, having an owl as her symbol.   I had one Naturalist tell me once that owls came to represent wisdom because of their large eyes and their success in hunting at night and catching creatures that humans weren't able to detect.  Also their ability to twist their heads around to such a great degree could give the impression that they are "all seeing."  In other parts of the world (like some African countries and in some Middle Eastern cultures), owls are actually thought of negatively--that seeing one is an omen of death or something evil happening.