John of Sahagún was a 15th-century Spanish priest and Augustinian friar known for his powerful preaching. Born in Sahagún to a wealthy family, he initially held several ecclesiastical offices, including being a canon in Burgos. However, he later renounced these positions to live a life of poverty and strict devotion. After recovering from a serious illness, he joined the Order of St. Augustine. He became a celebrated preacher in Salamanca, where he frequently criticized the moral failings of the nobility and defended the rights of the poor.