We're going to be talking about this past weekend's episode of Game of Thrones for a long time — it was a war epic and a dramatic tour de force, filled with palpable ambition. But this isn't the first time a single episode of television has redefined what's possible in the medium.

Here are 10 single episodes of science fiction and fantasy shows that changed television forever. To help put this list together, we talked to Javier Grillo-Marxuach, creator of The Middleman and writer for some of our favorite shows. (Grillo-Marxuach has contributed to io9 before.) What follows is a synthesis of our own ideas and his.

1) Buffy the Vampire Slayer, "The Body"
The episode in which Buffy loses her mother and we cope with the aftermath of loss and grief is spare and unforgiving, without even any music. The supernatural aspects are pushed to the margins, as humans and superhumans alike cope with the mystery of pure, unleavened death.

2) Doctor Who, "City of Death"
This Douglas Adams-scripted episode is a huge departure stylistically from the usual Doctor Who of the late 1970s, from the slick Paris location filming to the wistful piano music. It feels like a sophisticated comedy film rather than just another adventure, and the sharp dialogue and clever use of time travel prefigure everything Steven Moffat has done with the series in recent years.

3) Battlestar Galactica, "33"
The Galactica must jump into hyperspace every 33 minutes to avoid being destroyed by Cylons, and the strain begins to drive the crew to the edge of insanity. And meanwhile, the officers struggle with the decision of whether to destroy a civilian ship that's carrying nuclear weapons and failing to communicate. Says Grillo-Marxuach, "This may be the best first episode of a scifi series ever made, and probably the best first episode of any series, period. It set off a run of excellent episodes that was unbroken until the show's second season, and it established a series far more interesting and high-minded than the miniseries ever promised."

4) Star Trek, "Balance of Terror"
It's hard to pick one ground-breaking episode of the original Trek, a show whose format was revolutionary in general. But this one stands out as a great look at the reality of war, and a strong attempt to use all of the tactics and tropes of submarine combat in a space battle. This is one of the first depictions of space combat on television, and still one of the best. We see that there are good people on both sides of the battle, as well as xenophobic hotheads. Of all Trek's many allegories, this might be the best. We were also tempted to include a few TNG episodes, notably "The Best of Both Worlds," which includes more excellent space combat alongside cyborg body horror and a great look at what it means to be human.

5) The Twilight Zone, "Walking Distance"
A middle-aged executive stops at a service station near his home town, which appears not to have changed since he was a little boy — and winds up having a confrontation with his own childhood that makes him more aware of the burden of being an adult. Grillo-Marxuach calls this episode "the moment when that show became the single most canny indictment of American life in the age of the grey flannel suit — as well as the moment when it became clear that that series would influence everybody, from scifi to drama writers for decades to come."

6) Lost, "The Constant"
The island-castaway show had a number of standout episodes along the way, in which the mystical themes and character development were used in the service of a great story. But the one that people kept talking about, and learning from, afterwards was this season four outing where Desmond becomes unstuck in time and only one thing can save him from madness and death: connecting to Penny, his true love and the "constant" that ties his whole life together. This blend of emotion and a high concept still sticks in your mind and shows that television can be more than just a string of predictable story beats.

7) Blake's 7, "Pressure Point"
Blake's 7 looks even more dated than 1970s Doctor Who, thanks to bargain-basement special effects among other things. But it influenced your favorite adventure shows of the 1990s and 2000s, thanks to its morally gray, flawed characters and dark storylines. Especially this one, where the idealistic freedom fighter Blake goes off the deep end because he thinks victory is within his grasp. He lies, he cuts corners, he breaks his promises to his own crew — and the result is death. Few shows of that era killed off a major character, but fewer still would have dared to make that character's death unquestionably the hero's fault. When Blake sinks to his knees in despair, we know exactly how he feels.

8) The X-Files, "Clyde Bruckman's Final Repose"
A man who has the psychic ability to predict people's deaths faces his own, and it's a stylish, provocative piece of television. According to Grillo-Marxuach, this "is probably the episode of The X-Files that finally crystallized the show as not only a genre phenomenon but as a true piece of mainstream, zeitgeist-defining art."

9) Max Headroom, "Blipverts"
Says Grillo Marxuach, "The [Max Headroom] pilot, being a remake of a British tv movie and with its "blipverts" mcguffin, is [a] game changer, in that it basically introduced a cyberpunk aesthetic to American TV and made a very trenchant statement about consumerism. You can look at individual episodes of Max Headroom, but at the end of the day, the transition of a virtual personality from talk show/music video host in Britain to commercials, to an American TV series that used genre to affect so critical a posture against the medium itself, makes it a unique harbinger of both transmedia and postmodernity."

10) The Outer Limits, "Demon With a Glass Hand"
A man discovers that he's actually a robot sent back in time from the future, in this episode by Harlan Ellison. Grillo-Marxuach says the "double whammy" of this episode and "The Architects of Fear," in which scientists fake an alien invasion to stop a nuclear holocaust, has influenced "everything from Terminator to Watchmen."