Who is The Cavalier Avvocato Enea Silvio Carrega from The Baron in the Trees and what is their importance?

The Cavalier is illegitimate half-brother to the Baron Arminio, raised alongside Arminio by their father. He spends years in a Mohammedan country learning hydraulics and connecting himself in some unknown way with a woman named Zaira. Biagio never knows whether she is daughter or lover, only that Cosimo reports his calling her name when he knows he is preparing to meet his doom at the hands of the pirates. The Cavalier spends time as a slave, a prisoner and a bookkeeper in his life, and instead of making him worldly or colorful, these experiences turned him timid and withdrawn. He is talented in hydraulics and beekeeping, and Cosimo learns from him everything he can. He also, however, seems to deal in the shady affairs of pirates, and so meets his end when Cosimo exposes the pirates to the locals, and they take the Cavalier to be the traitor.