It's not too unusual for crossovers to occur in fiction, and they're normally the result of works having the same creative team or company. So Superman and Batman meet as they're both owned by DC Comics, for example. But there have been cases were little references were dropped that open up new and exciting, albeit confusing in some cases, story options for the fans, which technically can't be explored due to the clash of tones/licencing laws. Actual, proper crossovers will probably never happen... but it would be fun if they did. Here are four examples of unusual shared universes that I have discovered.
- Star Trek/Sherlock Holmes
But, in Star Trek VI: The Undiscovered Country, aka "the One Where They Literally Go Looking For God", Leonard Nimoy's Captain Spock states,
"An ancestor of mine maintained that if you eliminate the impossible, whatever remains – however improbable – must be the truth."This is in fact a paraphrasing of one of Holmes' famous quotes, first said in Sherlock Holmes novel The Sign of Four, published in 1890, but long since absorbed into the popular consciousness since. The film seems to be implying that Spock is related to Holmes, possibly through his human mother... but the idea of Holmes being a Vulcan stranded in Victorian Era London and passing the time with cocaine and crimefighting is something of a funny image.
- Alien/Predator/the Wildstorm Universe (Pre-Reboot)
This is all good and insular, and despite a couple of non-canon crossovers with the likes of Batman, the Terminator, Judge Dredd and the like, the two alien species didn't really have any lasting effect on any franchises but their own... BUT, there was one exception: namely, the Xenomorphs were used as the means to end Warren Ellis' Wildstorm series Stormwatch. This was done by the UN-mandated superhero team's space station getting infested with the aliens, numerous major characters getting infected/killed in the process, and eventually leading the organisation's dissolution after a member of the group sacrifices himself by piloting the station into the Sun.
The story would have made for a good, if some what depressing, one-shot crossover like the Batman etc. examples above... except that the Xenomorph invasion of Stormwatch was not only kept canon up until the dissolution of the imprint fairly recently, but it also lead to the creation Warren Ellis' next Wildstorm title and arguably it's most infamous team. This comic was the Authority. So the Authority owes its existence, at least partially, to a crossover with the Alien and Predator franchises. Which is... a little strange, frankly.
- Doctor Who/Hitchhikers' Guide to the Galaxy
This connection to one of the UK's favourite science fiction writers was then referenced by David Tennant's Doctor in the first of the rebooted series' Christmas specials, the aptly named Christmas Invasion, where the newly regenerated, dressing gown-clad Doctor casually mentions meeting Arthur Dent, the protagonist of the Hitchhikers books.
Could the Doctor Who and Hitchhikers franchises exist within the same continuity? Ehhh, up to a point. Definately more in the Russel T. Davies Era than the current one, as it seemed to share a similar sense of humour where dealing with the science fiction aspects of the show. I wouldn't really know how the events of each series would line up with each other though, but internal really continuity is something that is handled somewhat fast and loose by the Doctor Who team anyway so that's not really any problem.
- GI Joe/Transformers
Despite what you might think, there have been a lot more crossovers between Hasbro's two non-Pony related franchises than you'd imagine. For one thing, it's been kind of established that the two series' share the same universe and have directly effected each other's continuity at least twice.
The first time occurred during the Transformers cartoon, where an ageing Cobra Commander showed up with all his trademark subtle delivery and behaviour,
This could, again, be seen as a one off crossover, except the two franchises keep on bumping into each other, even with Cobra being responsible for rebuilding Megatron in a new green and purple tank form at some point amongst other things.
More of the crossovers can be found in Linkara's Transformers review below,
- Lord of the Rings/the Chronicles of Narnia
The same is true even back in the day, when JRR Tolkien and CS Lewis were apparently very good friends and often commented upon each other's work. But considering how different their forms of fantasy stories are, with Tolkien's built like a world created by a fan of myth and folklore and Lewis' built in a more casual, writing for children manner with religious references stuck on, is there any any chance of a connection between the two franchises?
Well actually yes, in a round about way. You see, Tolkien and Lewis were both members of a group of writers called the Inklings, and as such they had some access to each other's work before it was actually published. So although the Hobbit was published prior to World War Two, Lewis had access to some of the notes that would later be used to write Lord of the Rings, and as such decided to reference his friend's work in his own. So within CS Lewis' Space Trilogy they referenced several pieces of Middle Earth history was historical fact, for example, with Merlin being the inheritor of magic from Tolkien's Atlantis analogue: Númenor (though Lewis accidentally spelt it Numinor).
So Middle Earth sort exists in the distant past of some of Lewis work, but does that connect to Narnia? Well, in Middle Earth geography, there is apparently a void beyond the edge of with world, and Tolkien said that there was the possibility of other worlds existing connected to his one... but he never wanted to explore it further. So I guess that it's possible that the two might be connected further, like with the connecting space between worlds in the Narnia canon, the Wood Between the Worlds, but nothing more concrete than that sadly.
- Good Omens/the Bromeliad/the Johnny Maxwell Trilogy
The connections here are a lot more simple, as they are three works that are, mainly, by just one person, that exist in the same universe despite the major differences in tone. First there is Good Omens, a collaborative novel made by Terry Pratchett and Neil Gaiman, which is both a parody of End of the World fiction as well as the religious horror genre. Then there are Terry Pratchett's lesser known series': the Bromeliad, which is a trilogy about a group of tiny people who eventually discover that they're aliens, and the Johnny Maxwell Trilogy, which is about a boy having encounters with aliens, ghosts and time travel, in that order.
Fairly straight forward this: The Johnny Maxwell books are based in the Midlands town of Blackbury, as are the Bromeliad books, with even the department store that makes up the location of the first of the latter trilogy getting a mention in the Maxwell books at some point. The second Maxwell book, Johnny and the Dead, involved a company called United Amalgamated Conglomerated Holdings attempting to buy and build on a local graveyard, and the ghosts inhabiting it being somewhat put out by this. United Amalgamated Conglomerated Holdings could possibly be related to United Holdings (Holdings) Ltd, the company that gets involved in a near lethal paintballing match near the beginning of Good Omens.
- Black Lagoon/Law and Order/Luther/the X-Files/Tons of Other Shows
The anime show Black Lagoon, which deals with organised crime, piracy and the like in mid-Nineties Thailand, has a character called Revy. She's a Chinese American woman who operates as a pirate and has a number of warrants still out for her arrest back in her hometown of New York City, specifically for murdering a policeman belonging to the 27th Precinct (considering they show WHY she murdered him in the final episode of season three of the show, I can't honestly say I blame her).
Most of them are crime dramas, for example, and not just ones from the US. The BBC detective show Luther, which starred Idris Elba, referenced the detective, with the line: "Send the details to Detective Munch in Special Victims Unit, New York." He also appeared in the French version of Law and Order: Criminal Intent.
Back in the US, he appeared in the Wire, Arrested Development,the Beat, Homocide: Murder on the Streets, the X-Files... Really if any show runs long enough, Munch will probably show up or get mentioned at some point... and now an anime crime series can be added to the list of possibilities. Weird.