The Egyptian priest you are referring to is
Arius.
Arius argued that Jesus was a created being, subordinate to God the Father. He believed that Jesus was divine, but not of the same essence (homoousios) as the Father. This view was in direct conflict with the emerging orthodox Christian belief that Jesus was fully God, co-eternal and of the same substance as the Father.
His teachings sparked widespread controversy, leading Emperor Constantine to call the First Council of Nicaea in 325 AD. The council condemned Arius's views as heresy and formulated the Nicene Creed, which affirmed the divinity of Jesus and his equality with the Father. The Nicene Creed uses the term *homoousios* ("of one substance") to describe the relationship between the Father and the Son, directly countering Arius's teaching.
You have a slight typo in your question. The council was called Nicaea, not "Nivea".