If you're talking about all time, Isaac Newton (1643-1720). Not only did he create the first field theory, but he invented the calculus to do it. Where would physics be without differential equations? If you're talking about today, I doubt there's a consensus.
It is not fair to say that Newton created the first field theory. The explicit expression of the field concept usually goes to Faraday. For Newton, there was an instantaneous interaction at a distance between bodies. He by the way expressed his dislike about the "instantaneous", but why the instantaneous works so well is a long story. Aberration and the Speed of Gravity
"Nature" or "myself" are both good answers, in that the term "authority" is quite inappropriate in mathematical physics. One can only learn mathematical physics by practice.