He is the twin brother of John Constantine's grandfather, Lance Corporal William Constantine, who died at the battle of Somme. Both him and his brother survived the birth, unlike most Constantine twins , which resulted in his feelings of inadequacy. Charles is a WWI veteran, who refused to kill an unarmed german soldier, and was subsequently punished for his insubordination by his commanding officer, who shot him in the groin, effectively castrating him, which only contributed to his feeling of unworthiness.
In 1920 he is touring Europe with his companion, a wealthy and eccentric heiress who claims she cannot die, and chooses a new name and identity every single day. The two become a target of the Corinthian, who is trying to learn how to kill, so he could become a true nightmare in the real world. After Corinthian kills the girl, Charles finally finds the killer instinct and self-confidence that he's been missing all his life, and kills that incarnation of the Corinthian. He is subsequently seen leaving Venice on a train, seeming much calmer and at peace with himself.