Well in the comics Constantine is a Brit from Liverpool who looks a bit like Sting, so right off the bat not so "true". I was checking my facts at Wikipedia and noticed they call him a "superhero".
The Legends version might have been closer to the version of Constantine that became a part of the DC Supers universe and who is a member of the Justice League Dark--but the Vertigo version of the character was quite a bit different. He had a Machiavellian approach to his work and did what needed to be done to accomplish the "mission" even if that meant sacrificing his friends or innocents. He wasn't so much a magician/sorcerer as a guy who had a knowledge of magic--he was more of a strategist and a con-man and defeated demons through sheer wit much more often than with the use of magic. The price he paid was a deeply emotional one. He was plagued by guilt over the things he had to do to keep demons and evil at bay in the world and self-medicated through the heavy use of alcohol. The first hundred or so issues of the Vertigo series are excellent and highly recommended. EDIT: I should mention that, in my opinion, despite the superficial differences I have always thought that Keanu does a pretty good job of interpreting the personality of Constantine. Sure, he does look the part but he gets much closer than Matt Ryan did. Although, if the original Hellblazer pilot before it was reworked hints that Ryan could also have been a pretty accurate JC if he had been given better material to work with.
He was kind of there from the beginning since he was introduced in Swamp Thing around the time of Crisis of Infinite Earths. The first several years weren't Vertigo, which wouldn't become a thing until 1993. He still would pop up on the DC side from time to time.
That's true. He was a Moore creation, originally part of Swamp Thing's supporting cast and didn't even have a proper name initially. That's why I specifically referenced the "Vertigo" version, which is the one most people are referring to when they discuss the "real" character.
The Matt Ryan version wasn't so different from that. On his NBC show, they set up a dynamic where he had a chance to escape damnation if he did good deeds, so he had a selfish motive to try to act a bit more heroic than he otherwise would, but he still did hurt and sacrifice and screw over his friends repeatedly. And in Legends, despite the show overall going more for comedy, Constantine was allowed to go plenty dark and make really big mistakes and selfish choices. I mean, he only joined the Legends in the first place because he was using them to hide out from a threat he'd brought on himself, which basically meant lying to them and putting them in harm's way to protect his own skin.
I thought he was called "John Constantine" from the get go. But it has been years since I've read Moore's Swamp thing. Hellblazer was around for like six year before Vertigo. I think a lot about John was established in that time.
Granted I only know early Hellblazer Constantine but I never really though of Matt Ryan as a definitive Constantine. He always seems nicely cleaned and pressed except for his tie being loosened to a precise amount. I mean he's British and has light hair but he never really seemed to inhabit the character to me. Maybe if I went back to the NBC episodes but CW Constantine seemed a very sanitized take on the character, Constantine-lite. Are the later comic appearances closer to that?
I think they both sanitized the character to an extent, in different ways. For instance, NBC wouldn't let him be bisexual, but The CW did. They both danced around his smoking; the NBC show mostly avoided it but managed to get a bit of it in toward the end, and in Legends he was often trying to light up but getting interrupted, or the like. They both established that he was a right bastard and was toxic to the people around him and was far from heroic by nature, but they both put him on redemptive arcs that made that more a part of his past he was trying to move beyond. In Constantine, like I mentioned, they gave him the incentive of getting exempted from damnation as his carrot to motivate him to do good deeds, for entirely selfish reasons. And in Legends, he had the other Legends providing a positive influence or keeping his excesses in check. Neither show was free to go as far as the Vertigo comics (or what I gather they did), but they did what they could to be true to the character within the limits they were under.
I could be remembering incorrectly because its been almost forty years, but I recall we learned his initials JC originally without learning his name. Fans speculated that he was supposed to be Christ. I'm not sure if it was only his first appearance or longer before we learned his full name. EDIT: I would agree with the CW/NBC version being Constantine-Lite--which is similar to how he's presented when he is with the Justice League Dark or other heroes. The Vertigo version is the more intense version but essentially the same personality--Constantine was always a "hero" in the sense that he believed in saving the world and people from the occult and demonic, but he was utilitarian in his logic. If a baby had to be fed to a demon in order to save Bristol then he would sacrifice the baby if it were a last resort-- if there were any way he could save Bristol and save the baby then he would do that. (I invented that scenario.) The big difference is that the Vertigo Constantine would con or trick the demon because he couldn't go toe to toe with it using magic.
It could be because I was a fan of the character in comics, but my first thought was, "oh god, why?" For a more Hellblazer version of John, check out the animated feature "City of Demons". Matt Ryan did the voice. I really liked him on both the NBC and CW shows, though they definitely toned him down.
IIRC, City of Demons was initially announced as taking place in the Arrowverse, but it quite obviously didn't, offering very different interpretations of characters like Astra and Chaz. I think it is meant to be in continuity with the Justice League Dark animated movie where Ryan also played Constantine, which makes it part of the overall animated-movie continuity that was going on at the time.
Honestly, the comics Constantine was hard to swallow. I found the movie version a bit more sympathetic. I'm intrigued enough.
The problem is that if it wasn't for the Constantine movie, most folks wouldn't even know Constantine existed and odds are he'd not have been okayed to appear in other DC shows later on. So it's a double edged sword.
I honestly doubt anybody thinks they're even the same character unless they're already fans. I read the comics and it wasn't until much later that I discovered that's who Keanu was meant to be (I didn't see the movie but remembered thinking the trailers weren't that special at the time)
Don't the movie and TV versions of Constantine pronounce his name differently, "-tine" and "-teen"? And it's the movie version that gets it right, I gather.
Just his detached way he would sometimes conduct himself. He always had some sort of secondary motive, and rarely felt like someone you could trust.