Is God the author of evil?
NO, God is not the author of evil. I would say that God is the author of some things that become evil, and yes, He knows in advance. We also have to distinguish between an evil nature and evil acts. When we are created, we have an evil nature even though we have not yet done any evil.
The only "things" which can become evil are people and angels and certainly both have and will become evil (because they have free will). Animals, rocks, the ocean, books, movies, a bottle of booze etc cannot become evil in and of themselves but as we all know, they can become destructive or provide what the Latins call the "near occassions of sin" because all creation has been distorted by sin.
The Foreknowledge possessed by God has always been posited by The Church on account of the transcendant nature of God. What exactly that means, when we accept that God "exists" in a way which assuredly isn't anything like what we understand as "existence", we of course don't know. The best we can say is God is "O WN"
"We also have to distinguish between an evil nature and evil acts. When we are created, we have an evil nature even though we have not yet done any evil."
FK, if we are created with an evil nature, then God is indeed the author of evil, and yet neither you nor I nor many of the people here believe that, so how can this be?
Jo Kus in #478 presents the Latin view of the state of Man after the Fall as Kosta has of the Orthodox theology earlier on. Neither, at base, speak of man as being born with an evil nature. As Kosta points out, The Church believes that man is born with a "propensity" to sin, a propensity to do evil but not with an inherently sinful nature. God created man with the propensity to become like Him, in other words, with the potential for theosis. Adam, through an exercise of his free will, sinned and that sin, and the sins which multiplied thereafter, so distorted the nature of man that he was no longer in a state of potential theosis, which is the true Life, but rather a captive of death. Man in that situation could do nothing for himself. God did not create this, man did. Man screwed and screws up. God is perfect; He never screws up. Think, when you look out over the world, how our sins and our sins alone have distorted all creation, what we have done to God's perfect work!
When the Word became Flesh by the Incarnation, lived, died, broke down the gates of hades and "annihilated death", preaching Life to those in the tombs, He restored to us the possibility of regaining our pre Fall state and fulfilling our created purpose which is theosis, not death. For this reason The Church has called Christ the "New Adam".