Introduced to Parisian society by the Count, ​Marquis Andrea Cavalcanti quickly earns the respect and admiration of the bourgeois, through the showy exhibition of his fortune and dandified airs. He displays a romantic interest in Eugénie, who openly despises his character and is repulsed by his very presence.

Spoiler

Cruel and sadistic, Cavalcanti manipulates Danglars into giving him the hand of Eugénie in marriage, once Albert's nobility is proven to be a ruse. At his wedding, it is revealed that Cavalcanti was once a criminal by the name of Benedetto, rescued from execution by the Count who provided him with wealth and a title. He is also the illegitimate child of Gerard Villefort and Victoria Danglars, abandoned after birth to keep their affair a secret. A twisted individual with sociopathic tendencies, Calvancanti not only attempts to marry (and rape) his half-sister (Eugénie), but also seduces (and beds) his own mother (who was unaware that he was her son at the time).

(Source: Wikipedia).