Adventures with Swamp Thing (1985-1988)
Constantine was introduced in the pages of THE SAGA OF SWAMP THING, in which he served as "occult advisor" and companion to the titular muck monster. In THE SAGA OF SWAMP THING #37 (1985), John first contacted the creature, and the two struck up a friendship that would last for years. John provided some answers to the Swamp Thing about his origin, revealing that he was in fact an elemental, powered by the mystical force known as the Green. John later introduced the Swamp Thing to the Parliament of Trees, a mystical body of plant elementals (SWAMP THING #47, 1986).
Constantine spent much of his time trying to help Swamp Thing work as the protector of the Green, but the two came into conflict when Swamp Thing wished to leave his duties behind and pursue a relationship with his wife. Unwilling to find compromise and seeing no benefit to himself (aside from, of course, the aversion of global catastrophe if the Green were to go unprotected), John stopped pressing the issue. But things between John and Swamp Thing became even more strained when the latter possessed and used John's body to conceive a half-human child with his wife.
The Hellblazer (1988-2013)
After initially appearing with Swamp Thing, John was given his first solo ongoing series, Hellblazer. Here John became increasingly haunted by the ghosts of his past, both literally and figuratively. Members of his old gang, the Newcastle Crew, began cropping up in various states of supernatural duress, looking for John's help. His solutions, however, were often less than ideal, and the long line of bodies that trailed him wherever he went grew all the longer.
Eventually, John came into conflict with two groups, the Resurrection Crusaders and the Damnation Army (HELLBLAZER #4, 1988), which brought Constantine face to face with Nergal, the demon he’d summoned at the start of his career.
In the ensuing battle, John's soul was displaced from his body and entered the astral plane (allowing his aforementioned possession by Swamp Thing). Upon returning to his corporeal form, John faced off against Nergal yet again, and was able to successfully defeat him, though not without damning himself in the process. Personifications of Agony and Ecstasy warned John that, upon his death, the minions of Hell would come to collect him.
John's solo adventures continued for years, with the Hellblazer growing ever more disillusioned with the idea of altruism. He eventually hatched a scheme to sell his soul to different lords of Hell at the same time in an effort to save himself. It was a gambit that would force the lords to keep Constantine alive, lest they be forced to engage in all-out war for his soul upon his passing. This resulted in John, who was always a heavy smoker, tricking these cosmic forces into curing him of life-threatening lung cancer (HELLBLAZER: DANGEROUS HABITS, 1994).
The New 52 (2011-2016)
Following 2011’s Flashpoint event, Constantine became one of the lead members of Justice League Dark, a team comprising occult-based DC Super Heroes who specialized in handling supernatural crises.
Much of John's status quo was unchanged following the events of DC UNIVERSE: REBIRTH #1. He rejoined old allies such as Swamp Thing and set about lifting an old curse that had been put on him to make him physically ill every time he set foot in London, where he now often operates.