Who is Lion from Tides of War: A Novel of Alcibiades and the Peloponnesian War and what is their importance?

Polemides' younger brother, Lion is an eager soldier, who enlists in the army before he is old enough. He is descirbed as brave and noble. In the end, Lion dies a heroic death after being enslaved in the Sicilian quarries, where he continued to fight his captors.