Simon Magus

The figure the heresiologists insisted was the fountainhead of everything they hated — a Samaritan wonder-worker who appears briefly in Acts 8 trying to buy the power of the Spirit (hence "simony"), and who in later hostile accounts travels with a woman named Helena said to be the fallen Thought of God, redeemed from a brothel in Tyre.

Almost certainly a construction. He matters because he shows the heresiologists' method: build a single ancestor for every position you dislike, and the variety of your opponents becomes a family tree of error.