I love the expression on his face :)

The Utrecht painter Johannes Moreelse worked for a few years in Rome, where he was influenced by the paintings of Caravaggio. He painted scenes in the style of Caravaggio, with unidealised half-length figures and big contrasts between light and dark.

The grinning man in this painting represents Democritus, the laughing philosopher. He is laughing at the vanity of mankind and the transience of the world. Democritus forms a pair with Heraclitus, the weeping philosopher. Moreelse made several versions of the two philosophers.

Museum info:
https://www.mauritshuis.nl/en/our-collection/artworks/705-democritus-the-laughing-philosopher/