All the evils of the world are due to lukewarm Catholics.
-Saint Pope Pius V
In only six years as Pope, Saint Pius V reformed the clergy in Rome, standardized the Holy Mass through the 1570 edition of the Roman Missal (which would remain unchanged for nearly 400 years) , declared Saint Thomas Aquinas a Doctor of the Church, formed the Holy League, and pushed back against the growing protestant revolts of the time to protect Italy.
Born as Antonio Ghisleri on January 17th, 1504, Saint Pius V grew up in the town of Bosco in the Duchy of Milan. At 14 he entered into the Dominican Order with the name Michele and was ordained a Priest at Genoa in 1528. After his ordination he was sent to Pavia to serve as a lecturer for the next 16 years. During a time of loose morals he insisted on strict discipline among the clergy, especially among his Dominican brothers. Very quickly he gained a reputation for his discipline, piety, and ascetic lifestyle. In 1550 he was elected to the commissariat of the Holy Office and in 1556 made Bishop of Sutri by Pope Paul IV. The role of Bishop also included being selected as inquisitor of the faith for Milan and Lombardy.
Saint Pius V fulfilled this new role eagerly. After a year serving as Bishop he was made a cardinal and named Inquisitor General. His opposition to Pope Pius IV's decision to admit Ferdinand de'Medici to the Sacred College led to his dismissal from the Vatican and the removal of his authority as inquisitor. On his return to Piedmont, Pope Pius IV died and the conclave began the election of a new pope. On January 8th, 1566, Saint Pius V was elected and was crowned on his 62nd birthday by the protodeacon.
Almost immediately the new Pope set out to restore discipline to Rome. Residency was compelled for clergy and the liturgy of the Mass elevated and it's importance restored. The 1570 Roman Missal Saint Pius V promulgated was mandatory throughout the church and remained unchanged until Pope Paul VI's revision in 1969. It is known today as the Tridentine Mass. After declaring Saint Thomas Aquinas the fifth Latin Doctor of the Church, Saint Pius V commissioned the first edition of opera omnia and had it produced in 1570 at the studium generale of the Dominican Order at Santa Maria sopra Minerva. Pope Pius V is also credited with the origin of white garments worn for the Papacy.
In the midst of challenging reforms, Saint Pius V also was instrumental in forming the Holy League against the Ottoman Empire. During his canonization after his death, several witnesses attested that Saint Pius V miraculously knew of the League's victory against the Empire during the Battle of Lepanto despite being in Rome at the time. In France, to combat the Huguenots, he directed the dismissal of Cardinal odet de Coligny and seven bishops, nullified the royal edicts tolerating Reformer services and introduced the Roman catechism. In England he declared Queen Elizabeth I a heretic and released her subjects from any allegiance towards her. In response, Queen Elizabeth began an active campaign of persecutions against the Catholics in England whom she viewed as traitors.
It is believed that Pope Pius V dealt with some form of cancer later in his life. He died on May 1st, 1572 and was buried in the chapel close to the tomb of Pope Pius III. His remains were later transferred to a monument in the chapel of SS. Sacramento in the Liberian basilica. During the process of canonization, his body was placed in a new tomb erected in the Sistine Chapel of the Basilica di Santa Maria Maggiore. Pope Clement X beatified him in 1672 and Pope Clement XI formally canonized him on May 22nd, 1712.
While his feast day was originally set with the rank of Double for May 5th, it was moved during the 1969 revision to April 30th.