Miguel Servetus (1511–1553) was a Spanish theologian, physician, and humanist who challenged both Catholic and Protestant orthodoxy. Born in Villanueva de Sigena, Huesca, he studied theology, law, and later medicine, developing a reputation as a scholar and physician. Deeply influenced by the Reformation of Luther, he published radical works such as De Trinitatis Erroribus (1531) and Christianismi Restitutio (1553). His theological writings earned him enemies across Europe, including John Calvin, with whom he exchanged hostile relation and correspondence. Beyond theology, Servetus made groundbreaking medical contributions, notably describing pulmonary circulation, anticipating modern cardiovascular physiology. Arrested in Geneva in 1553, he was condemned for heresy and burned alive with a copy of his book. Servetus is remembered as a martyr of free thought and a pioneer in medicine.