Constantine already lives rent free in my head but my lastest kick of reading about heresies has me hating on Augustine just as much.

After the state endorsement of Christianity, there were a bunch of social climbers who jumped aboard the label without really caring about the teachings. A 4th century British theologian named Pelagus criticized this tendency and emphasized free will and the importance of moral behavior, including redistribution of wealth to the poor. He taught that humans are born sinless, and it is theoretically possible (if extremely difficult) to live a sinless life.

He is a Christian

    who shows compassion to all,
    who is not at all provoked by wrong done to him,
    who does not allow the poor to be oppressed in his presence,
    who helps the wretched,
    who succors the needy,
    who mourns with the mourners,
    who feels another's pain as if it were his own,
    who is moved to tears by the tears of others,
    whose house is common to all,
    whose door is closed to no one,
    whose table no poor man does not know,
    whose food is offered to all,
    whose goodness all know and at whose hands no one experiences injury,
    who serves God all day and night,
    who ponders and meditates upon his commandments unceasingly,
    who is made poor in the eyes of the world so that he may become rich before God.

At the time, the dogma of original sin had not been established and was a controversial new idea that ran against early Christian beliefs, but it was successfully championed by Augustine. By claiming that it was impossible to achieve salvation by living a moral life, but rather only through the grace of God, it emphasized the importance of the clergy as providing the only access to salvation via sacraments - a factor which was explicitly expressed in the judgement against Pelagus - which laid the groundwork for the selling of indulgences. It also established extremely weird positions like that everyone who died never having heard of Christianity, including unbaptised infants, were automatically sent to Hell. But hey, Roman PMCs could rest easy knowing that they just had to go through the motions and respect the church's authority rather than doing anything crazy like freeing their slaves or something. Meanwhile, he more or less embraced predestination, which was cited extensively by John Calvin (and eventually leading to the modern Catholic teaching which is that God places you in circumstances where he knows ahead of time if you'll pass or fail, but this is different from predetermining your fate... somehow).

So much of this shit is still so relevant because so many people take these beliefs for granted with no consideration of the material influences and interests driving their development.