A Neoclassical onyx cameo set in a gold ring. Demosthenes.

This fine and large oval onyx cameo depicts the figure of the Greek philosopher Demosthenes. He is represented, standing in slight three-quarters, wearing the classical 'toga'. The figure is masterfully sculpted with great rendering of the anatomical volumes under the drapery. 
The face shows the classical physiognomy of the philosopher depicted in the ancient marble portraits.
Possibly after, a Roman marble statue of a citizen. Before 1818, it was converted to a likeness of the orator Demosthenes, in the Römisch-Germanischen Museum, Cologne (Germany). 

Demosthenes (b. 384–d. 322 BCE) was one of the leading public figures in Athens in the third quarter of the 4th century BCE—a statesman who led the Athenians in their ultimately unsuccessful struggle against Philip of Macedonia, as well as the greatest of ancient Greek orators