Arianism is the sub-christian heresy that asserts Christ, who is the Second Person of the Trinity, is in fact a created being or – depending upon the variety of Arianism- became deified at some point in time. Because of this belief, Arians often hold that Christ, who is God the Son, is lesser than – in a deified sense – God the Father.
This heresy is named after its founder, Arius (AD 250-336). Arianism was deemed a heresy by the council of Nicaea in 325. That judgment was reiterated at the Council of Constantinople in 381.
Historically, Arians included Goths and Vandals (AD 500-700), the Polish Brethren (circa AD 1550) and today include Unitarians, Jehovah’s Witnesses and the 7th Day Church of God.