St. John Leonardi was born in Tuscany, Italy in 1541, during the time of upheaval in the Church due to Martin Luther. He studied to be a pharmacist, then became a priest. As a young priest he devoted himself to teaching catechism to youths. In 1574, he founded the Order of the Clerks Regular of the Mother of God of Lucca, a congregation of diocesan priests. He suffered many tribulations for this work, including exile. His contemporary, St. Philip Neri, was a great friend and spiritual guide, and helped him particularly in his time of exile.

Gradually his influence as a champion of the Catholic faith against Protestantism became known throughout Italy. He later founded in Rome what became the Institute De Propaganda Fide (Society for the Propagation of the Faith) and the Confraternity of Christian Doctrine for the promotion of the Catholic Faith and the formation of missionaries. St. John Leonardi died at Rome, in 1609, the victim of his devoted care for the sick and plague-stricken.

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