Hermit, b. 1419, at Sahagún (or San Fagondez) in the Kingdom of Leon, in Spain; d. 11 June, 1479, at Salamanca; feast 12 June. In art he is represented holding a chalice and host surrounded by rays of light. John, the oldest of seven children, was born of pious and respected parents, John Gonzalez de Castrillo and Sancia Martinez. He received his first education from the Benedictines of his native place. According to the custom of the times, his father procured for him the benefice of the neighbouring parish Dornillos, but this caused John many qualms of conscience. He was later introduced to Alfonso de Cartagena, Bishop of Burgos (1435-1456) who took a fancy to the bright, high-spirited boy, had him educated at his own residence, gave him several prebends, ordained him priest in 1445, and made him canon at the cathedral. Out of conscientious respect for the laws of the Church, John resigned all and retained only the chaplaincy of St. Agatha, where he laboured zealously for the salvation of souls.
Finding that a more thorough knowledge of theology would be beneficial, he obtained permission to enter the University of Salamanca, made a four years' course, and merited his degree in divinity. During this time he exercised the sacred ministry at the chapel of the College of St. Bartholomew (parish of St. Sebastian), and held the position for nine years. He was then obliged to undergo an operation for stone, and during his illness vowed that if his life were spared, he would become a religious. On his recovery in 1463, he applied for admission to the Order of Hermits of St. Augustine, at the church of St. Peter, at Salamanca, and on 28 Aug., 1464, he made his profession.
He made such progress in religious perfection that he was soon appointed master of novices, and in 1471 prior of the community. Great was his devotion to the Blessed Sacrament, and at Mass he frequently saw the Sacred Host resplendent in glory. He was gifted with special power to penetrate the secrets of conscience, so that it was not easy to deceive him, and sinners were almost forced to make good confessions; he obtained wonderful results in doing away with enmities and feuds. In his sermons he, like another St. John the Baptist, fearlessly preached the word of God and scourged the crimes and vices of the day, though thereby the rich and noble were offended. He soon made many enemies, who even hired assassins, but these, awed by the serenity and angelic sweetness of his countenance, lost courage. Some women of Salamanca, embittered by the saint's strong sermon against extravagance in dress, openly insulted him in the streets and pelted him with stones until stopped by a patrol of guards. His scathing words on impurity produced salutary effects in a certain nobleman who had been living in open concubinage, but the woman swore vengeance, and it was popularly believed that she caused the saint's death by poison (this statement is found only in later biographies). Soon after death his veneration spread in Spain.
The process of beatification began in 1525, and in 1601 he was declared Blessed. New miracles were wrought at his intercession, and on 16 Oct., 1690, Alexander VIII entered his name in the list of canonized saints. Benedict XIII fixed his feast for 12 June. His relics are found in Spain, Belgium, and Peru. His life written by John of Seville towards the end of the fifteenth century with additions in 1605 and 1619, is used by the Bollandists in "Acta SS.", Jun., III, 112.
(Taken from Catholic Encyclopedia)