Solomon
Proverbs 25:3ESV·traditional attribution

As the heavens for height, and the earth for depth, so the heart of kings is unsearchable.

Matthew Henry Presbyterian @wholebiblehenry

Here is, 1. An instance given of the honour of God: It is his glory to conceal a matter. He needs not search into any thing, for he perfectly knows every thing by a clear and certain view, and nothing can be hidden from him; and yet his own way is in the sea and his path in the great waters.

Commenting on Proverbs 25:2-3

John Gill Reformed Baptist @doctorgill

The heaven for height, and the earth for depth,.... These are eminent for what are ascribed to them; nothing is higher than the heavens, nor anything deeper than the earth; the height of the heavens cannot be reached, and the centre of the earth cannot easily be got unto; the heavens above cannot be measured, and the foundation of the earth cannot be searched beneath...

Jamieson-Fausset-Brown Reformed @jfbcommentary

Ye wisely keeping state secrets, which to common men are as inaccessible heights and depths.