Gregory the Dialogist

Whom else hath He appointed over the earth, or whom hath He placed over the world which He hath made? In order, namely, that thou mayest understand, No one. For He governs indeed by Himself the world which He created by Himself: nor does He need the aid of others in governing, Who needed it not for creating. …

Morals on the Book of Job, Book XXIV ↗

Thomas Aquinas

He proves there is no injustice in God first from the fact that if God were unjust, one would not find justice anywhere, since the universal judgment of all men pertains to him, and so he says, "What other has he constituted on the earth?" as if to say: Is it to be believed that someone was constituted by God to judge all the earth justly if he is evil? Thus he says that one should not believe there is someone else to judge the earth because the same person is the maker and the governor of the earth. …

Commentary on Job ↗