The DC Cinematic Universe is going to be a thing. Even after the Euthanization of the Nolan-verse (released in theaters under the name Dark Knight Rises). Even after the sphincter-clenching disaster of Ryan Reynolds' Green Lantern, originally intended to be the official genesis of the project. Even after Man of Steel, where a nation collectively turned to the person next to them hoping to gauge what their own response should be before offering a tentative “I guess so”. There is simply too much theoretical money to be made from a Marvel-style shared movie universe to be ignored. The DC Cinematic Universe is going to be a thing.
And so, the sequel to Man of Steel seems to have been elected by Warner Brother's shareholders as the introduction of the DCCU's Batman (with all of the consternation that caused) and at least a cameo for the DCCU Wonder Woman (with all of the consternation that caused), so this really does seem like the tone the whole endeavor will have: dark, funereal, shunning the conventions of the “cartoonish” comics while eagerly embracing the outlandish conventions of blockbuster popcorn cinema. Every bit the spiritual successor of the Dark Knight trilogy. Okay, I can live with this.
In that context, I humbly propose that Vin Diesel is the perfect man to play the J'onn J'onzz, Martian Manhunter. Here's why:
I won't be spending a lot of time on Diesel himself. The specific casting in this case is less important than the message it sends about how the Martian Manhunter should be portrayed. Diesel's been in enough movies that you can make up your own mind if his grumbly mumbly tough-guy routine is or isn't your cup of tea. The Martian Manhunter is not the only alien in the Justice League, but he is certainly the most alien. Distant. Possessed of inhuman emotions. A cipher onto which we can affix our own fears or our compassion. And he shares this with many of the roles Diesel has already played. Setting aside the troubles of both franchises, Dominic Toretto of the Fast and Furious series and Riddick of... uh... Riddick are equal parts merciless thug, monster, loyal friend, protector, and savior. They are opaque characters, settled firmly in a moral gray. In my view, Vin plays them well. He can play it tough or he can play it soft, but there's always enough nuance to leave you guessing. And he was the Iron Giant, after all.
Originally, Martian Manhunter's secret identity was that of John Jones, a private investigator (or “manhunter” in the vernacular of the era). This has been lost in most adaptations of the Martian, and as far as I can tell hasn't featured that prominently in the character's recent comic history, either. But it should... or at least it could. The traditional fedora-tipping, trench coat-sporting John Jones would never fit in the self-consciously modern world of the DC Cinematic Universe, but what if he was less Dick Tracy and more Dog the Bounty Hunter?
Imagine the Martian Manhunter as a rough and tumble bail bondsman who hangs around dive bars and strip clubs, developing working relationships with those at the fringes of the criminal underworld. That's vastly different than the sort of sleuthing the Dark Knight typically does on the silver screen (i.e. “type at a computer until it tells Batman the answer” or “hit the person until he tells Batman the answer”). Considering that the Flash will most likely be a CSI lab tech in his day job, having a “detective” who cares less about physical evidence and more about motive and human intelligence would make for a nice contrast within the Justice League ensemble. It also gives the Martian Manhunter a role in the inevitable “team squabbles” that usually boil down to Batman's moral ambiguity and Superman's idealism. Rather than the usual wide-eyed detachment of the character, this is a Manhunter that might actually have strong convictions about crime-fighting methods.
The Martian Manhunter has been a staple in DC's team books for decades and recent animated team television and movies, but there's not a lot of material focused exclusively on him, and even that is usually about his place in the history or future of Mars. Considering the dour tone of Man of Steel, I'm not sure I'd really like them to spend a second movie franchise dwelling on the extinction of an entire planet. We've seen Warner Brothers take a blind stab at “ambitious space epic” in Green Lantern, and no one wants to see that again. Even the image of a lone philosophical figure pacing through the red dust of Mars has already been done recently by WB and Zack Snyder in the Watchmen.
Unless it got completely reconnected somewhere along the way that I'm not aware of, the story of the Manhunter's arrival on Earth is, well... dated to say the least. J'onn is transported to Earth by a lone scientist by accident via a machine that really wasn't intended to do that. Once stranded on Earth, he decides to fight crime because why not. That's about it. It's the sort of five-page excuse-to-get-the-premise-rolling that dominated the Silver Age, but wouldn't make for the most engaging film. Without going down the rabbit hole of “what would make a good movie according to me”, I'd just suggest that maybe the circumstances of the Martian's arrival on Earth could be left vague or even unknown. The origin story, in this case, is him learning to live among humans, growing toward a friendship with one or a few specific humans, then something traumatic (kidnapping, murder, or other conflict) leads him to properly become a “manhunter”. Basically, imagine if E.T. decided to became a crime-fighting badass instead of phoning home.
Can a more traditional incarnation of J'onn work on film? Sure, but would he work in the upcoming DC Cinematic Universe? Based on the recent attempts of Warner Brothers to adapt their comic book properties (placing special emphasis on Green Lantern and Man of Steel as their intended foundations) and the news that has come out about Batman vs. Superman, I don't think so. The technicolor J'onn J'onzz of the comics, with his occasionally humorous capers, doesn't seem to belong with Henry Cavill's grim Superman in the washed-out blue cityscape of Zack Snyder's Metropolis. The Martian's sensitive introspection likely wouldn't fit with a Wonder Woman played by Gal Gadot, whose previous roles have been in films that are decidedly superficial. By all appearances, Warner Brothers is building the DCCU around the baser appeals of flash-in-the-pan actors and uninspired directors that don't know the difference between “epic” with “long”. Where the third act is reserved for a noisy, confusing, tedious CGI battle. Where Jesse Frickin' Eisenberg is somehow Lex Luthor... *Ahem*
In short, if Warner Brothers tried to do the traditional Martian Manhunter now, I'm sure they would screw it up. But I think they can manage the compromised, action-oriented, more accessible version I suggested above, and that's definitely Vin Diesel. This is the Case for a Completely New Take on the Martian Manhunter or more accurately:
“How I Learned to Stop Worrying and Love the Lens Flare”