Jacob Palaeologus, also called Giacomo da Chio, was a Dominican friar who renounced his religious vows and became an antitrinitarian theologian. A polemicist against both Calvinism and Papal Power, Palaeologus cultivated a wide range of high-placed contacts and correspondents in the imperial, royal, and aristocratic households in Eastern Europe and the Ottoman Empire; while formulating and propagating a radically heterodox version of Christianity, in which Jesus Christ was not to be invoked in worship, and where differences between Christianity, Islam, and Judaism were rejected as spurious fabrications. He was continually pursued by his many enemies, repeatedly escaping through his many covert supporters.

Ferenc Dávid was a Protestant preacher and theologian from Transylvania, the founder of the Unitarian Church of Transylvania, and the leading figure of the Nontrinitarian Christian movements during the Protestant Reformation. He disputed the mainstream Christian doctrine of the Trinity, believing God to be one and indivisible.