He is a doctor of the Church, and converted a great number of protestants back to the faith.
This is from Amazon:
"After being repeatedly rebuffed in his attempts to re-evangelize Calvinist Protestants who would not listen to Catholic preaching for fear of reprisals, St. Francis resorted to writing leaflets and inserting them into copies of his sermons, then posting them on walls, slipping them under doors and handing them to anyone he could. Four years later almost 72,000 had returned to the ancient Catholic Faith! These tracts have been gathered together and entitled The Catholic Controversy. The works are still as fresh and powerful today and give some of the most cogent arguments against Protestantism ever penned, presenting a defense of the Catholic Faith that in some respects has never been equalled."
If you (like me) have many protestant relatives, it can be a good time to start a novena for his intercession, so that they may find the true Church of Christ.