Spanish physician who was trained in Paris. He believed that God is unitary and that the Trinity is not founded in scripture. He anonymously published Restitution of Christianity, a book outlining his theological views, but was forced to change his name to avoid persecution from the church when his authorship was discovered. John Calvin one of the most powerful of the early Protestants, was especially angered. Servetus fled for Italy, traveling through Geneva, which was under Calvin's control. Calvin had Servetus arrested, and condemned him to burning at the stake.

Besides the heretic theological views presented in his book, Servetus also proposed that the blood traveled from the heart through the pulmonary artery and back through the pulmonary vein, without actually passing through the septum. Servetus's views on circulation, argued on theological grounds, were ignored until Harvey extended the theory.