Contention: A key portion of Christianity theology (the nature and two parts of the trinity) is passed down to us as a made-up word by a semi-pagan man with some pretty heinous moral character traits. As most know, the man is the Roman Emperor Constantine, who was trying to make all religions welcome in his Empire to keep the peace within his borders as much as possible. In response to some mounting discord within the Christian community regarding the nature of Jesus, for the First Ecumenical Council the bishops were summoned to Nicea by Constantine who, as Emperor, considered himself above all other men but below both the pagan gods and the Christian God. When trying to decide whether Jesus was less than God or equal there was much disagreement. Constantine first tried the approach of asking people to just keep their views in the privacy of their thoughts. When quite a few bishops protested, he personally intervened to suggest a made-up Greek word to describe Christ and God as being 'of the same substance', which would fudge the issue and offer something everyone could get behind.
As for semi-pagan, Constantine never gave up his pagan religious title of Pontifex Maximus, retained in his service a pagan augur (diviner) and considered himself the leader of both pagans and Christians.
Regarding his moral character, Constantine during this time killed off both his son-in-law and his grandson. He also boiled his wife Fausta alive in her bath.
Primary source material from: "Ancient Worlds: A Global History of Antiquity" by Michael Scott (2016).