John Duns Scotus

Franciscan John Duns Scotus (c. 1266 – November 8, 1308) was ...

... a theologian, philosopher, and logician. Some argue that during his tenure at Oxford, the systematic examination of what differentiates theology from philosophy and science began in earnest. He was one of the most influential theologians and philosophers of the High Middle Ages, nicknamed "Doctor Subtilis" for his penetrating spirit ...
- Wikipedia

Read more about John Duns Scotus at Thomas Williams's site (University of Notre Dame) and at Research Group John Duns Scotus