Okay, first of all, I'm talking about stuff that actually happened in the comics.
Second of all, you misunderstood. Emperor of Man John Constantine is the twin John killed in the womb, "golden boy." In the world in which the other twin was born, he was named John Constantine, and became the most powerful magician ever and to know him was to love him, and to not know him was to love him from afar, and he used his magical talent for probability manipulation (with which he could troll the gods themselves) to mess with his twin brother from another universe.
Yes, Golden Boy John Constantine was pretty much John "Mary Sue" Constantine, he even brought Earth into a golden age.
He gave John lung cancer for example. Since that's an example of Golden Boy John Constantine showing his affection, kind of leads one to believe he probably has something to do with John being a reverse King Midas- everything he touches turns to shit.