Science fiction and fantasy are all about discovering the new and the strange — but if you travel far enough and boldly enough, eventually you'll get a certain sense of... deja vu. But that can be a good thing.

Plenty of science fiction and fantasy's most successful works have, er, borrowed somewhat liberally from earlier works. But they've also made some improvements on the works they lifted from. Here are 10 copies that actually improved on the works they were copying.

Top image via Mandy Maria on Flickr.

Disclaimer: When we say a story copied something else, we're not saying the derivative work is totally unoriginal. Just that it owes a rather large debt. And when we say that something improved on the original work, we're not saying it's better than the original, overall — just that it added some cool and clever ideas to the concept.

10. The Matrix and The Invisibles
What did it borrow? Everything, according to The Invisibles' Grant Morrison, who's been very vocal about saying that the Wachowskis picked his pocket. In particular, the comic features a young man being recruited into a secret resistance that fights against the oppressive forces that control reality in secret.
How did it improve upon the original? Well, the last time I read The Invisibles, it felt... sprawling, to say the least. Morrison's comic, like a lot of his more ambitious work, is all over the map. The Wachowskis distilled it down to a fairly tight movie, in which reality is literally fake, and we're in a virtual reality simulation. (Lots of other people tried to do a "virtual reality" movie around the same time, and the Wachowskis deserve some props for being the only ones to have success with it.)

9. Firefly and Outlaw Star
What did it borrow? Reportedly, Joss Whedon himself has denied being aware of this 1990s manga/anime series, so take this one with a grain of salt. It's entirely possible that all similarities are coincidental. Still, people have pointed out a host of similarities, including the band of outlaws led by an anti-hero, with a childlike engineer. And the fact that there's a girl with mysterious powers, shipped naked in a box, who's being hunted by the government. But like I said, could just be coincidence.
How did it improve upon the original? Well, the genius of Firefly is that it takes genre tropes, like a lot of Western ideas, and flips them on their head. Almost everything about Firefly feels fresh, no matter how many antecedents you might point out, because the characters and the universe are so unique. You could show me a 1990s TV show with the exact same incidents as Firefly, in the exact same order, and it still wouldn't have those characters, including the fascinating backstory about the Browncoats and the Alliance. Firefly is original in a way that goes beyond the question of whether it has direct antecedents.

8. Harry Potter and The Sword in the Stone
What did it borrow? We covered this one a while back, and J.K. Rowling has pretty much admitted that Wart from T.H. White's novel is Harry Potter's "spiritual ancestor." Wart is a young boy who is destined to save England, who is taken in by a long-bearded wizard who keeps weird birds.
How did it improve upon the original? Among other things, the invention of Hogwarts is a touch of brilliance, and the backstory about Voldemort and Harry's parents is pure gold. More than anything, Rowling created a whole world, that millions of people want to live in.

7. Avatar and Everything
What did it borrow? Umm... everything? Actually, the accusations that Avatar burgled an entire neighborhood of source works are a little overstated, as we discuss here. But the similarities to Poul Anderson's Call Me Joe, Ursula K. Le Guin's The Word for World is Forest and several other works are striking. In particular, the evil humans ravaging the beautiful unspoiled world, and the guy being put into an artificially created body are old ideas.
How did it improve upon the original? Say what you want about Avatar, James Cameron created a relatable main character and put him into a beautifully detailed world. The amount of world-building in the film is breathtaking, and it forces us to care more about whether they're going to pave paradise and put up a parking lot. Also, the idea that the trees have neural connections is kind of sweet.

6. Alien and Voyage of the Space Beagle
What did it borrow? Enough that author A.E. Van Vogt reportedly sued — and Twentieth Century Fox settled out of court. In particular, the overall plot of Alien seems to draw on an incident from one of the two stories in Van Vogt's "fixup" novel, in which an alien named Ixtl implants parasitic eggs into humans. The humans are trapped on their spaceship with Ixtl and have to trick Ixtl into leaving.
How did it improve upon the original? A ton of ways — Alien is a classic of science fiction cinema because of its creepy atmosphere and knife-edge writing. In terms of genres, Alien is a brilliant proof of concept of the genre of space horror, while Space Beagle is pure space opera.

5. The Terminator and the Outer Limits, "Demon with a Glass Hand" and "Soldier"
What did it borrow? One of these Outer Limits episodes is about a guy who turns out to be a human who's put his soul into a robot to fight aliens. The other is about a guy who travels back in time from a nightmarish future, only to sacrifice his life to save his new-found family when an enemy travels back from the future. The ideas are similar enough that writer Harlan Ellison sued James Cameron, who settled out of court.
How did it improve upon the original? Well, for one thing, Cameron took those two wildly disparate ideas and turned them into a coherent story. It's one thing to come up with a time-travel from the future fighting another time-travel from the future, and a guy who's really a robot, and it's another to come up with The Terminator. For another, The Terminator has a great spin on the "future savior" idea, one which puts Sarah Connor at the center of the story.

4. District 9 and Alien Nation
What did it borrow? Some argue that one of 2009's best movies owes a huge debt to this 1980s TV series — in particular, the idea of alien refugees coming to our world and facing discrimination and difficult conditions.
How did it improve upon the original? District 9 is a lot more hard-hitting and edgy, with Wikus blithely slaughtering a whole shack full of alien babies in front of us, and hints that the aliens are about to be moved from a shanty town to a concentration camp. And just the character of Wikus is a fantastic invention.

3. 28 Days Later and Day of the Triffids
What did it borrow? According to director Danny Boyle, John Wyndham's 1951 novel was writer Alex Garland's original inspiration for this movie — particularly the bit where a man wakes up in a hospital bed, with his eyes bandaged, only to discover that the world's gone mad. The whole idea of a post-apocalyptic London where only a few people remain "normal," and predators lurk everywhere, is very Wyndham. Oh, and the attempts to create a new, repressive, society under siege.
How did it improve upon the original? The idea of the "rage virus" is totally new, and the innovation of "fast zombies" is a masterstroke. Both stories are creepy in very different ways — but 28 Days Later is stomach-turningly terrifying in parts.

2. Star Wars and Dune
What did it borrow? Here's a pretty good rundown from a group of Star Wars fans. Actually, George Lucas was quite a story magpie, lifting from The Hidden Fortress, The Dam Busters, Joseph Campbell, and tons of other sources. But the Star Wars saga owes a lot to Dune, including a desert planet, a hero who goes off the rails but redeems himself at the end, a messianic young man, a quasi-religious order that has almost supernatural powers. And so on.
How did it improve upon the original? The original Star Wars, in particular, is so beautifully executed and so full of energy, it's like nothing that came before it. Those space dogfight scenes, and the Battle of Yavin, are totally gorgeous. And a million details in the original film are just perfect. Including the Death Star, and the creation of a villain who's a literal shadow, Darth Vader. Image via Moongadget.

1. The Borg and the Cybermen
What did they borrow? This is what got me thinking about writing this piece in the first place. The similarities between Star Trek's cybernetic marauders and Doctor Who's formerly-human machine men are pretty striking. They're both pure biological beings who have become cyborgs and lost their individuality and emotions along the way. And they both very intent on finding people to convert into more of their kind. The Borg say, "You will be assimilated." The Cybermen say, "You will be like us."
How did it improve upon the original? As an old-school Doctor Who fan, it's hard to admit, but Who never really followed the implications of the Cybermen to their fullest extent, until the new series. Out of a dozen-odd Cybermen stories, only a handful of them even touch on the idea of the Cybermen trying to turn humans into Cybermen — it only actually happens on-screen in "Tomb of the Cybermen" and "Attack of the Cybermen." True to their nature, the Borg perfected the idea of a cybernetic race that reproduces by assimilating biological creatures. And the Borg added the idea of a hive mind, whereas the Cybermen lack individuality but still have to stand around talking to each other. Oh, and the Borg are creepier. Image by Benleto on Flickr.