Nontrinitarianism

Nontrinitarism is a movement that rejects the idea of the Christian Trinity. That idea says that God is three different persons in one being. 

There are several movements which can be classified as Nontrinitarian. At the First Council of Nicaea, in the year 325, people met and defined the idea of trinity. Some movements started before the council. Nontrinitarianism was later renewed in the Gnosticism of the Cathars in the 11th through 13th centuries, in the Age of Enlightenment of the 18th century, and in Restorationism during the 19th century.

Modern-day versions are usually called Unitarianism. 
 Jehovah's Witnesses do not believe in the Trinity and are known for showing people from the Bible why they believe the idea to be false.
Latter Day Saints (Mormons) also do not believe in the Trinity but believe that God the Father, his Son Jesus Christ, and the Holy Ghost are three separate beings, that are united in purpose.
Seventh-day Adventists did not believe in the Catholic doctrine of the trinity for the first 50 years of their existence either. The founders of the world wide Seventh Day Adventist Church believed that: "There is one supreme God of the universe and Jesus Christ: The only begotten Son of God!", Statement of Believes, 1873. The change came many years latter, when the founders of the Seventh Day Adventist Church had already 'slept in the Lord" (died).

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