What saint helped Saint Augustine in his conversion?

Augustine was a member of the Manichee branch of Christianity before joining the Catholic faith. As an Auditor, the lowest level in Manicheanism, Augustine never learnt the hidden mysteries, but he did learn the Manichean view of this evil world.

After transferring to Catholicism, he developed his views that man is inherently evil. He developed the doctrine of original sin, with the whole of humanity punished forever for Adam's sin of eating the forbidden fruit. In these views, he was inspired by Manicheanism, even though his understanding of that faith was necessarily only limited.