He was the author of the classic Introduction to the Devout Life.
Here is his life from Matins of his Feast,
Francis was born of devout and noble parents in the town of Sales, from which his family took its name. He was given a liberal education, devoted himself to the study of philosophy and theology at Paris and gained the degree of Doctor in civil and canon law at Padua. When he had been ordained priest and made provost of the church of Geneva, he carried out the duties of his office so well that Bishop de Granier sent him to preach the word of God in Chablais in order to win the inhabitants away from the heresy of Calvin. He undertook this mission with such great zeal and overcame so many dangers with the help of God that he is said to have brought back to the Catholic faith some seventy-two thousand heretics. When de Granier died, Francis was consecrated bishop. He founded a new order of nuns, named for the Visitation of the Blessed Virgin, and enlightened the Church with writings filled with heavenly teaching. At Lyon, he was seized by a grave illness and departed to heaven in the year 1622. He was declared a Doctor of the Universal Church by Pope Pius IX.And here is the article on him from the (old) Catholic Encyclopedia,
SAINT FRANCIS DE SALES, BISHOP, DOCTOR OF THE CHURCH—1567-1622
Feast: January 29
Francis de Sales was born at the Chateau de Sales in Swiss Savoy on August 21, 1567, and at his baptism in the parish church of Thorens was named Francis Bonaventura, for two greatly loved Franciscan saints. The room in which he was born was known as the "St. Francis room," from an old painting on the wall showing the friar of Assisi preaching to the birds; and it was this lover of all living creatures whom Francis de Sales was to choose as his patron in later years. His father, the Seigneur de Nouvelles, was an aristocrat who had served his country well in war and peace. On his marriage to the only child of Melchior de Sionnaz, who brought as her dowry the Signory of Boisy, he took the name of Boisy. When Francis was born, the eldest of thirteen children, his mother was only fifteen. The boy was frail at birth, but with devoted care he grew to vigorous maturity.(Read more...)