There are many great love stories in science fiction and fantasy. From Robin Hood and Maid Marian to Han Solo and Princess Leia, we all love the stories that end with some variation of "and they lived happily ever after."

But what about the great love stories that don't end happily? Because loss is just as universal a part of the human experience as love is, the combination of the two in one story is often that much more poignant. Here, then, are the top 10 best tragic love stories from geek fiction:

10. Anakin Skywalker & Padmé Amidala Skywalker – Yes, we know; we've seen Star Wars: The Trilogy We'd Like to Forget, too. We know there's about as much chemistry between the actors as between oil and water, so consider how the characters interact in the current Clone Wars TV series, where they (frighteningly enough) work much better together. And consider the underlying story: Anakin loves Padmé so much he's willing to rebel against everything else he holds dear because he believes it's the only way to save her. Regardless of how hopelessly naive he is, he does what he does out of love, and the fact that his actions ultimately kill her makes their story as tragic as they come.

9. The Doctor (as John Smith) & Joan Redfern – In one of the most heartbreaking episodes of David Tennant's run on Doctor Who, titled "Human Nature," the Doctor is forced to forget himself and become fully human in order to hide from aliens seeking to steal his Time Lord powers. After adopting the guise of a teacher named John Smith in England a year before the start of WWI, he falls in love with the school nurse, Joan Redfern. But the aliens ultimately catch up with him, and (in the next episode) to save her and everyone else, the Doctor is forced to restore his true nature and memories, and leave behind the love he had found. [Thanks to GeekDad Editor Ken Denmead for writing most of this entry, as he is far more knowledgeable about all things Doctor Who than I.]

8. Scott Summers & Jean Grey – Forget about the X-Men movies, because James Marsden gives the character of Scott Summers/Cyclops about as much personality as deck furniture. Now, granted, the character was never written terribly appealingly in the comic books, but you could at least believe that he and Jean were in love. We know that the whole Phoenix story got retconned such that Jean wasn't really Phoenix, and therefore was neither responsible for genocide nor dead, and that she "died" again, but for our money give us the original plot line. For us, Jean Grey was Marvel Girl, and Phoenix, and Dark Phoenix, and died on the moon in X-Men #137. The story as a whole, and particularly the love story, seems much more powerful that way.

7. Lee "Apollo" Adama & Kara "Starbuck" Thrace – If you watched the first two seasons of Battlestar Galactica (the reboot, of course), you saw that Apollo and Starbuck were, obviously to everyone but them, madly in love with each other. Which of course meant that, when each of them married someone else, you knew what was coming. To the writers' and actors' credit, you didn't necessarily want them to get together, because they both treated their spouses (and, to a certain extent, each other) like dirt while they carried on their affair, but you could see that it was inevitable. Then Starbuck went and died, and something Starbuck-like inexplicably came back from the dead. And you knew they still loved each other, even though you weren't sure (and, if you're like us, you still aren't) what Starbuck was when she came back. And then, in the final episode, just when it looked like they were going to live happily ever after, she vanished without a trace. That was probably the only time during the series we really felt bad for Apollo.

6. Buffy Summers & Angel – Could a love story get much more tragic than that between a vampire and a vampire slayer? It could in this case, with the vampire having a soul that he is cursed to lose if he experiences true happiness. Buffy ends up not only having to deal with Angel turning back to the evil Angelus, but on top of that has to kill him herself! When he ends up returning from hell, they continue their love story chastely, both knowing that it has no future.

5. Sarah Connor & Kyle Reese – Call it what you will: a love that was predestined to occur; a thinly veiled allegory of the story of Jesus (right down to the savior's initials); or a classic example of a time-travel paradox – it's still a great love story. Kyle saves Sarah's life from the Terminator over and over again, and the way they fall in love with each other as they fight to stave off the killing machine is much more believable than in most sci-fi films or action thrillers. You can sense from early in the film that Kyle is going to die before it ends, and that he knows it, which makes the story that much more tragic.

4. Sir Lancelot & Guinevere – As long as we're talking about tragic love stories, why not go really, really old school? It may seem strange to include an adulterous affair on this list, but in most versions of the Arthur legends, it is Lancelot that Guinevere truly loves, and not Arthur. One must assume that their love was very powerful, as they surely knew the consequences of being found out, and surely knew that their affair could not continue undiscovered for long. Ultimately (again, in most versions), it is Arthur who ends up dead as an indirect result of the wars that stem from their affair, and they meet one last time at Arthur's tomb, before Guinevere goes off to join a convent.

3. Dr. Horrible (aka Billy) & Penny – We Joss Whedon fans knew what we were getting into when we started watching Dr. Horrible's Sing-Along Blog online in 2008. We knew his proclivity for getting us to love a character, then killing that character without warning. So we shouldn't have been surprised by Penny's death in Act Three, but damn it if he didn't do it to us again. Once Dr. Horrible had exposed Captain Hammer for the self-important jackass he was, we really wanted to see him and Penny end up together, only to have her die in Dr. Horrible (Billy)'s arms, accidentally killed by the weapon he'd devised. Now, we may have to revisit this one after the sequel comes out, because all reports are that Felicia Day will be in it. Will she be reanimated by the good evil doctor? Only time will tell.

2. Captain James T. Kirk & Edith Keeler / Rayna Kapec – Jim Kirk, as you may have heard, was generally given to sleeping with anything that was recognizably female and attractive. But even he fell in love, at least twice that we're sure of, and both times tragically. The first time, in the great episode "The City on the Edge of Forever," Kirk falls in love with Edith Keeler, a woman from 1930s New York. Time-travel romances rarely end well, but in this case it ends far worse than usual, as Kirk not only has to let the woman he loves die but actually must stop Dr. McCoy from saving her, all to ensure that the Allies will have won World War II as they were supposed to. Then, in "Requiem for Methuselah," Kirk encounters the beautiful Rayna Kapec, the ward of a man named Flint who, it turns out, had at one time been Leonardo da Vinci, Mozart and lots of other brilliant men in Earth's history. Kirk falls in love with Rayna quickly and deeply, and she with him – which proves unfortunate, as she turns out to be a sophisticated android who, unable to handle her brand-new emotions and the choice between Flint and Kirk, dies. As the episode ends, in a rare display of compassion, Spock uses a mind-meld on Kirk to enable him to forget Rayna.

1. Peter Parker & Gwen Stacy – Regardless of what the Spider-Man movies would have you believe, it was Gwen Stacy who was Peter Parker's first true love. Gwen was pretty, but also smart and geeky like Peter, and we're sure to readers at the time it seemed inevitable that they would eventually get married. But it was not to be, with their relationship torn asunder first by Spider-Man's involvement in her father's death, and then, most tragically, by Gwen's murder at the hands of the Green Goblin. Her death was a watershed moment in comic book history as a whole, too, as it was the first time a hero had so completely failed to save his beloved.

So, what did we miss that should've made the top 10? Leave a comment.

Image: Arthur's Tomb: The Last Meeting of Lancelot and Guinevere by Dante Gabriel Rossetti