One could logically conclude that any individual who sells his soul to Satan in exchange for the opportunity to have sex with a fair maiden who views that individual through the prism of religious piety could be considered a Byronic hero. Ambrosio is the most revered man of cloth in Madrid, and considered as saintly as a monk could be. That he allows himself to be seduced by agents of Satan may not be entirely his fault, but that does not absolve him of responsibility for a chain of events that will include the rape and murder of the object of his sexual obsession, a girl of only 15 who he has imprisoned in a dungeon and visits regularly for the sole purpose of engaging in further acts of sexual depravity. That Ambrosio has long ago crossed the Rubicon of his own free will is evident in the following passage from Chapter 11 of The Monk:
“He doubted not, that being beyond the reach of help, cut off from all the world, and totally in his power, Antonia would comply with his desires. The affection which She had ever exprest for him, warranted this persuasion: But He resolved that should She prove obstinate, no consideration whatever should prevent him from enjoying her. Secure from a discovery, He shuddered not at the idea of employing force: If He felt any repugnance, it arose not from a principle of shame or compassion, but from his feeling for Antonia the most sincere and ardent affection, and wishing to owe her favours to no one but herself.”
Ambrosio’s kidnapping, rape and murder of Antonia endears him mightily to the devil, who has engineered this entire series of calamitous events. This once revered monk has succumbed to the very temptations that he condemned in others, and his hypocrisy is a source of great satisfaction to the keeper of his soul. In the novel’s final denouement, Satan condemns Ambrosio, castigating him for his weakness and sins, which, as it is revealed, were considerably greater than previously suspected:
'Wretch! you shall soon be with her! You well deserve a place near her, for hell boasts no miscreant more guilty than yourself. Hark, Ambrosio, while I unveil your crimes! You have shed the blood of two innocents; Antonia and Elvira perished by your hand. That Antonia whom you violated, was your Sister! That Elvira whom you murdered, gave you birth! Tremble, abandoned Hypocrite! Inhuman Parricide! Incestuous Ravisher! Tremble at the extent of your offences!”
So, Ambrosio has raped and murdered his younger sister, and murdered his mother. If that doesn’t qualify as the embodiment of the antihero, then nothing does.