Like so many throughout history, Constantine hated the god of the Jews,so he encouraged the Council of Nicea to alter things.
The most egregious thing that did was to call the gospels "the new Covenant".
They had to pick a unique name and.. I do not remember the lineage, but in the end, this "Jesus Christ" was a conglomerate of this Iesous and Christos.
I am not a scholar, but I have studied this deeply for my own personal edification.
Some time later the printing press was invented. Constantine commissioned this dude named Marcion to flood the market with Paul's writings.
That's when Constatine's "Paulinity" was born.