Solomon
Proverbs 20:27ESV·traditional attribution

The spirit of man is the lamp of the LORD, searching all his innermost parts.

Matthew Henry Presbyterian @wholebiblehenry

We have here the dignity of the soul, the great soul of man, that light which lighteth every man. 1. It is a divine light; it is the candle of the Lord, a candle of his lighting, for it is the inspiration of the Almighty that gives us understanding. He forms the spirit of man within him. It is after the image of God that man is created in knowledge.

John Gill Reformed Baptist @doctorgill

The spirit of man is the candle of the Lord,.... The rational soul of man is a light set up in him; this is what is commonly called the light of nature; it was a bright and burning light at first, but through sin is become a very feeble one; by which men have only a glimmering view of divine things, of God and his...

Jamieson-Fausset-Brown Reformed @jfbcommentary

The spirit . . . Lord--Men's minds are God's gifts, and thus able to search one another (compare Pro 20:5; Pro 18:8, Pro 18:17; Co1 2:11).