Pope St. Leo on Total Depravity

Pope St. Leo the Great ca. 400-461

[W]hereas the true Faith, which is the Catholic, acknowledges that the substance of all creatures spiritual or corporeal is good, and that evil has no positive existence; because God, who is the Maker of the Universe, made nothing that was not good. Whence the devil also would be good, if he had remained as he was made. But because he made a bad use of his natural excellence, and stood not in the truth Jn. 8:24, he did not pass into the opposite substance, but revolted from the highest good to which he owed adherence: just as they themselves who make such assertions run headlong from truth into falsehood, and accuse nature of their own spontaneous delinquencies, and are condemned for their voluntary perversity: though of course this evil is in them, but is itself not a substance but a penalty inflicted on substance. (Letter 15.7)