William Of Ockham
William of Ockham (also Occam) (ca. 1285-1349) was a Franciscan friar and philosopher from Ockham, Surrey. He studied Theology at Merton College, but left without obtaining his Master's degree due to disagreements with members of the theology faculty. Perhaps now most famous for Occam's Razor, he is regarded by many as one of the greatest logicians of all time.
Accused of heresy, Ockham was summoned to Avignon by Pope John XXII in 1324, where he became drawn into the debate between the Franciscans and the Papacy on the doctrine of apostolic poverty, eventually condemning the Pope as a heretic. (At this point, you should go and read Umberto Eco's The Name of The Rose.) He fled Avignon and was given protection by Louis IV of Bavaria, probably being excommunicated in the process. He spent the remainder of his life writing about political issues, eventually dying in a convent in Munich.