Girolamo Savonarola, OP (UK: /ˌsævɒnəˈroʊlə/, US: /ˌsævən-, səˌvɒn-/; Italian: [dʒiˈrɔːlamo savonaˈrɔːla]; 21 September 1452 – 23 May 1498), also referred to as Jerome Savonarola, was an ascetic Dominican friar from Ferrara and a preacher active in Renaissance Florence. He became known for his prophecies of civic glory, his advocacy of the destruction of secular art and culture, and his calls for Christian renewal. He denounced clerical corruption, despotic rule, and the exploitation of the poor.

In September 1494, when King Charles VIII of France invaded Italy and threatened Florence, Savonarola's prophecies seemed on the verge of fulfillment. While the friar intervened with the French king, the Florentines expelled the ruling Medicis and at Savonarola's urging established a "well received" republic, effectively under Savonarola's control. Declaring that Florence would be the New Jerusalem, the world centre of Christianity and "richer, more powerful, more glorious than ever", he instituted an extreme moralistic campaign, enlisting the active help of Florentine youth.

In 1495, when Florence refused to join Pope Alexander VI's Holy League against the French, the Vatican summoned Savonarola to Rome. He disobeyed, and further defied the pope by preaching under a ban, highlighting his campaign for reform with processions, bonfires of the vanities, and pious theatricals. In retaliation, Pope Alexander excommunicated Savonarola in May 1497 and threatened to place Florence under an interdict. A trial by fire proposed by a rival Florentine preacher in April 1498 to test Savonarola's divine mandate turned into a fiasco, and popular opinion turned against him. Savonarola and two of his supporting friars were imprisoned. On 23 May 1498, Church and civil authorities condemned, hanged, and burned the bodies of the three friars in the main square of Florence.

Savonarola's devotees, the Piagnoni, kept his cause of republican freedom and religious reform alive well into the following century. Pope Julius II (in office: 1503–1513) allegedly considered his canonization. The Medici—restored to power in Florence in 1512 with the help of the papacy—eventually weakened the Piagnoni movement. Some early Protestants, including Martin Luther himself, have regarded Savonarola as a vital precursor to the Protestant Reformation.

Savonarola was born on 21 September 1452 in Ferrara to Niccolò di Michele and Elena. His father, Niccolò, was born in Ferrara to a family originally from Padua; his mother, Elena, claimed a lineage from the Bonacossi family of Mantua. She and Niccolò had seven children, of whom Girolamo was third. His grandfather, Michele Savonarola, a noted and successful physician and polymath, oversaw Girolamo's education. The family amassed a great deal of wealth from Michele's medical practice. After his grandfather's death in 1468 Savonarola may have attended the public school run by Battista Guarino, son of Guarino da Verona, where he would have received his introduction to the classics as well as to the poetry and writings of Petrarch, father of Renaissance humanism. Earning an arts degree at the University of Ferrara, he prepared to enter medical school, following in his grandfather's footsteps. At some point, however, he abandoned his career intentions.

In his early poems he expresses his preoccupation with the state of the Church and of the world. He began to write poetry of an apocalyptic bent, notably "On the Ruin of the World" (1472) and "On the Ruin of the Church" (1475), in which he singled out the papal court at Rome for special obloquy. About the same time he seems to have been thinking about a life in religion. As he later told his biographer, a sermon he heard by a preacher in Faenza persuaded him to abandon the world. Most of his biographers reject or ignore the account of his younger brother and follower, Maurelio (later fra Mauro), that in his youth Girolamo had been spurned by a neighbour, Laudomia Strozzi, to whom he had proposed marriage. True or not, in a letter he wrote to his father when he left home to join the Dominican Order he hints at being troubled by desires of the flesh. There is also a story that on the eve of his departure he dreamed that he was cleansed of such thoughts by a shower of icy water, which prepared him for the ascetic life. In the unfinished treatise he left behind, later called "De contemptu Mundi" or "On Contempt for the World", he calls upon readers to fly from this world of adultery, sodomy, murder, and envy.

Savonarola studied Augustine and Thomas Aquinas. He also studied the scriptures and memorised parts. On 25 April 1475, Savonarola went to Bologna, where he knocked on the door of the Friary of San Domenico, of the Order of Friars Preacher, and asked to be admitted. As he told his father in his farewell letter, he wanted to become a knight of Christ.

In the convent, Savonarola took the vow of obedience proper to his order, and after a year was ordained to the priesthood. He studied Scripture, logic, Aristotelian philosophy and Thomistic theology in the Dominican studium, practised preaching to his fellow friars, and engaged in disputations. He then matriculated in the theological faculty to prepare for an advanced degree. Even as he continued to write devotional works and to deepen his spiritual life, he was openly critical of what he perceived as the decline in convent austerity. In 1478 his studies were interrupted when he was sent to the Dominican priory of Santa Maria degli Angeli in Ferrara as assistant master of novices. The assignment might have been a normal, temporary break from the academic routine, but in Savonarola's case, it was a turning point. One explanation is that he had alienated certain of his superiors, particularly fra Vincenzo Bandelli, or Bandello, a professor at the studium and future master general of the Dominicans, who resented the young friar's opposition to modifying the Order's rules against the ownership of property.