David
Psalm 81:9ESV·traditional attribution

There shall be no strange god among you; you shall not bow down to a foreign god.

John Calvin Reformed @genevareformer

PSALM 81 This psalm consists of two parts. Whoever was its author, he exhorts the people to remember the unparalleled grace of God towards them, in delivering them by his outstretched arm, and choosing them to be a kingdom of priests, and a peculiar Church to himself; that thus they may be excited devoutly to honor their deliverer, both by celebrating his praises, and by leading a holy life.

Commenting on Psalm 81:1-16

C.H. Spurgeon Reformed Baptist @princeofpreachers

There shall no strange god be in thee. No alien god is to be tolerated in Israel's tents. Neither shalt thou worship any strange god. Where false gods are, their worship is sure to follow. Man is so desperate an idolater that the image is always a strong temptation: while the nests are there the birds will be eager to return.

Matthew Henry Presbyterian @wholebiblehenry

God, by the psalmist, here speaks to Israel, and in them to us, on whom the ends of the world are come. I. He demands their diligent and serious attention to what he was about to say (Psa 81:8): "Hear, O my people! and who should hear me if my people will not? I have heard and answered thee; now wilt thou hear me?

Commenting on Psalm 81:8-16