Depends in part how you define medieval. Cola de Rienzi (1313-1354) was a clever son of poverty in Rome who was taught Latin and read the works of Livy and other Roman historians. Inspired by stories of the Gracchi brothers and their populist support of the down trodden at the expense of the elites, he formed his own political power base and managed, for a time at least, to upset the ruling baronial families (criminal syndicates, if we're honest). He styled himself in the old Roman manner as tribune. Of course it couldn't last and he, like the Gracchi, was eventually lynched - you can see a statue to his memory on your left as you climb the steps up to the Piazza di Campidoglio in Rome, marking the spot where he died. But his inspiration (aside from righteous outrage) was straight from Latin texts. So you see, there really is a case to be made for a classical education.

A good quick contemporary bio of de Rienzi is The Life of Cola de Rienzi, translated by John Wright.