Charles Constantine was twin brother of William Constantine (& thus the grand-uncle of John Constantine).
One of the few Constantine twins to survive, he always felt impotent during his life. Even though he (like his twin brother) had signed up to fight when Britain declared war against Germany in WWI, he had refused to kill which had led to a confrontation with his commanding officer, who shot him in the groin, effectively castrating him.
In the 1920s while in Venice with his female companion (who was unafraid of killing), he came across the Corinthian whom he learns he had first met on the battlefield during WWI and who now wants to learn how to kill. Although Charles was unable to do this for the Corinthian, his companion does. It is only after the Corinthian kills his companion that Charles finally kills someone (although it was only one of the Corinthian incarnations).
