John Constantine is a fictional character created by writer Alan Moore for the comic series Swamp Thing in 1985. He is a British occult detective and con man known for his cynical attitude and mastery of magic. Constantine often battles supernatural forces and demons, using his wit and intelligence to navigate dangerous situations. He is the protagonist of the Hellblazer comic series, which explores his struggles with morality, addiction, and the consequences of his actions. Constantine has appeared in various media, including films, television series, and animated adaptations, becoming a popular figure in the DC Comics universe.