Moses
Genesis 18:1BSB·traditional attribution

Then the LORD appeared to Abraham by the Oaks of Mamre in the heat of the day, while he was sitting at the entrance of his tent.

John Calvin Reformed @genevareformer

1. And the Lord appeared unto him It is uncertain whether Moses says, that God afterwards appeared again unto Abraham; or whether, reverting to the previous history, he here introduces other circumstances, which he had not before mentioned. I prefer, however, the former of these interpretations; namely, that God confirmed the mind of his servant witha new vision; just as the faith of the saints requires, at intervals, renewed assistance.

Matthew Henry Presbyterian @wholebiblehenry

The appearance of God to Abraham seems to have had in it more of freedom and familiarity, and less of grandeur and majesty, than those we have hitherto read of; and therefore more resembles that great visit which, in the fullness of time, the Son of God was to make to the world, when the Word would be flesh, and appear as one of us. Observe here, I.

Commenting on Genesis 18:1-8

John Gill Reformed Baptist @doctorgill

And the Lord appeared unto him in the plains of Mamre,.... That is, to Abraham; and very likely this appearance of God was quickly after the affair of the circumcision, to show his approbation of his ready obedience to his command; and at this time he was in the plains, or at the oaks of Mamre, the oaken grove there, as has been observed on...