Like Judaism, Unitarians believe in one G-d. They stress the oneness and unity of G-d. A famous Unitarian Christian is, for example, Sir Isaac Newton.
This Christian sect emerged in Poland during the Reformation period. Their founder was the Spanish theologian Michael Servetus, who criticized the Trinity in his book De Trinitatis Erroribus (On the Erroneous Understanding of the Trinity 1531). In short, they believe Jesus was a Jew who was inspired by G-d. Jesus was only human. They are in a word Antitrinitarian monotheist.
 The early Christian Arians agreed. Unitarians also reject the Christian concept of original sin as well as predestination.