Augustine solved the problem of evil by arguing evil isn't a thing at all
If God is all-good and all-powerful, why does evil exist? Augustine's answer, after abandoning the dualist religion of his youth, was that evil has no substance of its own — it's simply the absence or corruption of good, the way darkness is just the absence of light. God didn't create evil; evil is what happens when a good creation falls short of what it should be.