Is being immortal illegal?
Probably not as such, but living longer than the standard three-score and ten, as many superheros in both major multiverses are wont to do, does create some interesting legal issues.
I. Successive alter-egos
As a preliminary matter, if our immortal has decided not to make his immortality known to the general public, he’s going to need an alter ego, some of the difficulties of which are discussed here. But being immortal adds another wrinkle: you’re going to have to do this on a regular basis. You’ll basically have to ditch your original identity once it becomes clear that you aren’t aging, and then you’ll probably need to do it again every ten to twenty years to avoid the obvious “Why haven’t you aged in the last decade?” sorts of questions. This means completely severing ties with people who don’t know your true identity and coming up with a completely new alter-ego, from scratch, every decade or two.
That compounds the difficulties, because in addition to the standard this-is-a-fraudulent-activity-anyway problems, you’re now replacing a fictional identity with another fictional identity. The odds of someone noticing something strange don’t go up with repeated brushes with the law.
In pre-modern times, this wouldn’t actually have been that big of a deal. Public records were basically non-existent, and proving that you were who you said you were was not really something the law looked too closely at. But with the advent of modern recordkeeping and property registries, this becomes much, much more difficult.
II. The Rule Against Perpetuities
Immortality also raises the specter of a now mostly abandoned feature of property law doctrine which is nonetheless used to torture first-year law students to this very day, the Rule Against Perpetuities. The RAP dates back to early-modern England, when it was realized that aristocratic families were so encumbering their properties with conditions on inheritance that it was becoming impossible to transfer good title to vast swaths of the countryside. In response, the courts imposed a rule that no interest was valid unless it could “vest,” i.e. become a present interest in a living person, within twenty-one years after the death of some person alive when the interest was created. In short, you’re allowed to create interests which vest in your kids, but you can’t perpetually encumber your property such that your grandkids won’t have clear title to the property.
What exactly are we talking about? Well consider a family farm. Say mom ‘n pop are sentimental about the farm, so they leave the farm to their son but put some conditions on it, like so: “To our son, we leave the family farm, but if he ever stops using it as a farm like we did, the farm will revert to the estate.” That would be permitted by the Rule Against Perpetuities, but an attempt to pass that restriction on to their as-yet-unborn grandchildren would probably not.
A lot of states have abandoned the RAP, as hereditary land dynasties are no longer de regeur, and simply administering the RAP was a pain in the neck. Law students are still taught it, more often than not, but no one really runs into this in practice.
Which in the context of any of the comics multiverses wouldn’t necessarily matter, as immortality would play merry hell with the property law even with the RAP. An immortal could easily put all sorts of restrictions on property he sells over the course of his unnaturally long life, creating right of reentry in himself. And because he isn’t going to die, that land would never, ever be able to used for something he didn’t permit, because it is impossible to grant better title to land than you yourself possess, ergo any restrictions placed by an immortal would remain on the property forever. This is clearly less than ideal, and though most superheros would persumably not be dicks about this, one can easily imagine a supervillain really mucking things up that way over time.
III. The Fee Simple and Alter-Egos
But that aside, the actual nature of the fee simple also presents some problems. In normal society, a person accumulates property slowly over the course of their lifespan, perhaps inheriting some from their parents, and then passes whatever they haven’t managed to spend on to their children. It has been this way for all of human history, and even though some families manage to accumulate more wealth than others, but even the longest dynasties die out after a while. The House of Habsburg was the most powerful family in Europe for almost four centuries, but none of its heirs currently occupy any positions of particular influence, and their wealth pales in comparison to newer fortunes. The natural cycle of life and death has ensured a more-or-less orderly transition of property from parents to children since the dawn of time.
But an immortal person could simply go on amassing property forever. The perpetual nature of the fee simple and the power of compound interest mean that even starting from abject poverty, an immortal person could become quite wealthy in a century or two and could become one of the wealthiest in the world if given a thousand years. Exactly why Apocalypse didn’t simply buy every last scrap of available real estate as it came up for sale over the millennia is probably because that would have been boring, but as the best form of land use control is ownership, any number of nefarious plots would be a lot easier to pull off if you just bought the damn planet.
This presents two problems. The first is with anonymity, i.e. creating and maintaining a fictional person who is really one of the richest people in the world just doesn’t work. An immortal who wished to remain largely anonymous would find it difficult to do that while maintaining any significant level of wealth, contributing to the other problems with maintaining an alter-ego. This is not an entirely academic point, as at least some degree of wealth will be necessary to avoid being forced to get a real job. There’s a reason Batman, Tony Stark, etc. have playboy-billionaire alter-egos: it explains how they can afford to spend all of their time running around in exotic suits chasing villains. Being Batman is cool and all, but one of the defining characteristics of being a vigilante is that no one is paying you to do it.
Then there’s the simple fact that owning property requires interacting with it on some level, even if only through intermediaries, and the odds are decent that over the course of maintaining a financial empire, someone is going to notice that you look exactly like you did fifty years ago. Again, if you’re public about your identity, that’s fine, but if you aren’t, this will cause problems.
There are two obvious practical solutions to this issue. The first is to assume that being a superhero is really expensive, which it may well be. Batmobiles don’t come cheap. But Wolverine doesn’t seem to need much more than clothes, motorcycles, and beer to do his thing, so that isn’t a universal solution. The second is to simply be in the business of giving away lots of money on a regular basis so as to avoid accumulating more than a modest fortune. That’s risky–even real estate is no guarantee of future income–but it is potentially workable.
Of course, there’s always the option of faking your own death periodically–or actually dying–and either becoming your own heir or picking up a new, fabulously wealthy patron. That or a continuity reboot.
The second problem with adding immortality to the fee simple is that unless an immortal actually conquers the world, it seems doubtful that he would be permitted to acquire property ad infinitum. Someone is eventually going to notice. Then a bunch of someones, including various state actors, and there’s a good chance the latter will be pissed. Authoritarian governments certainly wouldn’t permit a private citizen to own large chunks of their real estate, and even democratic governments would probably wind up reaching a point where enough is too much. This would raise interesting Fifth and Fourteenth Amendment issues. Seizing or interfering with property interests generally requires compensation under US law, and trying to carve out an exception for that for immortal people who are just too damn rich would raise interesting Equal Protection and discrimination issues, some of which have been discussed elsewhere. But if political pressure were strong enough, the courts and/or legislature would presumably make something up.
So again, while being immortal doesn’t appear illegal as such, it does make keeping a low profile a bit more difficult, and the law would probably wind up making an attempt to literally capitalize on immortality more difficult than it sounds.