Fausto Paolo Sozzini, often known in English by his Latinized name Faustus Socinus, was an Italian Renaissance humanist and theologian, and, alongside his uncle Lelio Sozzini, founder of the Nontrinitarian Christian belief system known as Socinianism. His doctrine was developed among the Polish Brethren in the Polish Reformed Church between the 16th and 17th centuries, and embraced by the Unitarian Church of Transylvania during the same period.