Bonaventura Francesco Cavalieri (Bonaventura Cavalerius; 1598 – 30 November 1647) was an Italian mathematician and a Jesuate. He is known for his work on the problems of optics and motion, work on indivisibles, the precursors of infinitesimal calculus, and the introduction of logarithms to Italy. Cavalieri's principle in geometry partially anticipated integral calculus.
Born in Milan, Cavalieri joined the Jesuates order (not to be confused with the Jesuits) at the age of fifteen, taking the name Bonaventura upon becoming a novice of the order, and remained a member until his death. He took his vows as a full member of the order in 1615, at the age of seventeen, and shortly after joined the Jesuat house in Pisa. By 1616 he was a student of geometry at the University of Pisa. There he came under the tutelage of Benedetto Castelli, who probably introduced him to Galileo Galilei. In 1617 he briefly joined the Medici court in Florence, under the patronage of Cardinal Federico Borromeo, but the following year he returned to Pisa and began teaching Mathematics in place of Castelli. He applied for the Chair of Mathematics at the University of Bologna, but was turned down.
In 1620, he returned to the Jesuate house in Milan, where he had lived as a novitiate, and became a deacon under Cardinal Borromeo. He studied theology in the monastery of San Gerolamo in Milan, and was named prior of the monastery of St. Peter in Lodi. In 1623 he was made prior of St. Benedict's monastery in Parma, but was still applying for positions in mathematics. He applied again to Bologna and then, in 1626, to Sapienza University, but was declined each time, despite taking six months' leave of absence to support his case to Sapienza in Rome. In 1626 he began to suffer from gout, which would restrict his movements for the rest of his life. He was also turned down from a position at the University of Parma, which he believed was due to his membership of the Jesuate order, as Parma was administrated by the Jesuit order at the time.