Arius was a Cyrenaic presbyter, ascetic, and priest best known for the doctrine of Arianism. His teachings about the nature of the Godhead in Christianity, which emphasized God the Father's uniqueness and Christ's subordination under the Father, and his opposition to what would become the dominant Christology, Homoousian Christology, made him a primary topic of the First Council of Nicaea convened by Emperor Constantine the Great in 325.
If the Father begat the Son, he that was begotten had a beginning of existence: and from this it is evident, that there was a time when the Son was not. It therefore necessarily follows, that he had his substance from nothing.
If God and Christ were equal then Christ should be called God’s brother, not God’s Son.