Who is the clown that chased after Augustine?

The author of that statement may have been linking the white face clown with the characters in opera buffa (comic opera). The white face clown is the most intelligent of the clowns and is typically at the top of the pecking order. The whiteface clown will typically be the ringleader, who will order around the other clowns, and who has his 'clownishness' revealed either by his own ineptness or by that of his underling.

Opera buffa was made for and depicted common people with more common problems. Characters often wore white face paint, particularly when playing aristocrats, and the upper class was often parodied. In later operas, the white face paint ceased to play an important role.

There is also a theatrical performance style called whiteface, which parallels the style known as blackface (where whites wore black makeup in productions that often mocked blacks). However, that is not likely what is referred to in this particular phrase.

This phrase is likely referencing the chamber opera about Saint Augustine's life.