Theophylact of Ohrid
Catena Aurea · Johannesevangelium 1
There was a man sent from God, whose name was John. The same came for a witness, to bear witness of the Light, that all men through him might believe. He was not that Light, but was sent to bear witness of that Light.
Not an Angel, as many have held. The Evangelist here refutes such a notion.