Girolamo Savonarola was the guy who invented the practice of burning one's possesions in the name of Christ.
He was born in 1452 in the town of Ferrara. His family was well off, but he was an ugly kid, not well spoken, and he spent a lot of his time praying and meditating in private. His parents worried about him, and they encouraged him to travel, in hopes that it would shake him from his reverie. At the age of 21, he heard a bangup speech by an Augustinian preacher in Faenza, and it convinced him that it was time to renounce all worldly things. He immediately joined the Dominican Order at Bologna (odd that it wasn't an Augustinian Order, but the Dominicans were all the rage at the time). He didn't tell his parents.
He turned out to be a star student at the Order, and he was soon sent to Florence, to teach about the depravity of the Renaissance. This was in about 1481.
Florence was ruled at the time by Lorenzo de Medici (one of the Florence Medicis). This was "Lorenzo the Magnificent", benefactor of Leonardo DaVinci, Michaelangelo, and Botticelli, not "Lorenzo de Piero", to whom Niccolo Machiavelli was later to dedicate The Prince. Lorenzo was also a benefactor of the church, and the local Dominican monastery in particular, but that didn't stop Savonarola from speaking out against his rule. Lorenzo was a popular ruler though, and Savonarola had not yet hit his stride as a preacher, so not too many souls were saved. Savonarola went on the road, honing his apocalyptic chops, and by 1489, he was ready to take on Florence again.
Savonarola had always preached an ascetic line, but now his sermons were spiced with the imminent doom of the Revelation, and his message began to take hold. He railed against the 'pagan' artists of Florence, and the godless, hedonistic tyranny of their enabler, Lorenzo. Preaching from the pulpit of the San Marco monastery, which was within the Lombard Congregation of the Dominican Order, he began to draw huge crowds, and many of the most prominent citizens of Florence joined his following. Lorenzo thought Savonarola was rude and slightly crazy, but he continued to fund the monastery.
In 1492, Lorenzo called Savonarola to his deathbed for absolution. History and legend mix a bit here, but what is certainly true is that after Lorenzo's passing, Girolamo Savonarola became the de facto ruler of Florence, though Lorenzo's son, Pietro de Medici, was the prince.
The Dominican order separated the monastaries of Tuscany from the Lombards, and appointed Savonarola vicar-general of the new congregation. This was the time of the 'Bonfires of the Vanities'. He sent the children of Florence from door to door, collecting cosmetics, mirrors, fine clothes, and the like from Florentines who were conflicted about the humanism of the Renaissance, and the judgement of God that Savonarola told them it would bring down. He even convinced Sandro Botticelli (the "Birth of Venus" guy) to throw some of his paintings onto the fires.
Part of the appeal of his sermons was their strong populist streak, which was fine when old Lorenzo was around, but now he began lashing out at the corruption of the church, even attacking Pope Alexander VI himself. He started speaking well of Charles VIII of France, who, as coincidence would have it, was invading Italy, and eventually occupied Florence. Pietro and his kin fled, and when the dust settled and the French withdrew from the city, Savonarola was the spiritual leader of a kind of theocratic democracy in Florence. Christ, of course, was king. The Bonfires of the Vanities grew to piles sixty feet in height. Latin poets such as Dante, Boccaccio, and Petrarch were especially favored kindling.
Meanwhile, the rest of Italy, and Alexander VI's church, was not so happy with the French and their plans for the distribution of sovereignty among the Italians. An elaborate political dance ensued, with threats, blandishments, and other diplomatic measures deployed in dizzying succession. In the end though, both the Church, and the people of Florence tired of Savonarola's crap, and he was hanged and (appropriately, I suppose) burned in 1498.
Savonarola is a controversial figure in history, and there are some people who revere him for his devotion to faith, his steadfast resistance to authority, and his attachment to a version of democracy. I see him as a prototype of the modern dictator - playing on both the best and worst of peoples' instincts to accumulate power, and ultimately destroying himself, and the society he took control of.