Twenty-five years ago, the Terminator was resoldered, reprogrammed, and sent out to remorselessly terrorize movie screens for the second time. James Cameron’s Terminator 2: Judgement Day, released in 1991, was that rare mechanism: a sequel that both complemented and lived up to its director’s classic 1984 predecessor. The perfect killer of the future looked at the perfect killer of the past, and saw its perfect match.

There are two kinds of sequels. The first is the serial sequel—like the second Lord of the Rings film, or The Empire Strikes Back. In a serial sequel, the story of the first film is expanded or completed, so you find out whether Darth Vader survived and where Frodo went with that pesky ring anyway.

The second type of sequel is the repetition sequel—which is an encore rather than an extension. This includes films like Halloween 2 or Hostel 2 or…well, any slasher or horror sequel, really. The point of the repetition sequel isn’t to let you know what happened next. The point is to slaughter more people, because slaughtering the first round of people was so darn fun.

The genius of Terminator 2 is that it’s both a serial and a repetition sequel. The Terminator was in its essence an extraordinarily clever slasher film, with Schwarzenegger embodying all the Jasons and Freddies and Michaels who don’t “Feel pity, or remorse, or fear, and…absolutely will not stop, ever, until you are dead!”, as Kyle Reese (Michael Biehn) declares in one of cinema’s greatest overheated monologues. Terminator 2 keeps the same remorseless logic: two hours plus of the emotionless, resourceful, cyborg thing killing its way across the screen in an orgy of blood and chase sequences.

Many of the best lines and set-pieces of the first film are lifted for the second. In both, Arnold declares, “I’ll be back” before driving a vehicle into a building. In both, Linda Hamilton’s Sarah Connor is told by a terrifying stranger, “Come with me if you want to live!” In both, the denouement involves battered robot pursuer and broken human pursued dragging themselves through an industrial factory. The ominous clanking of huge machines in the present foreshadows the coming machines of the future, which will reduce humans to an irrelevant stain on the surface of a metal world.

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All the repetition works nicely with the films’ time travel themes. Just as the Terminator is sent back from 2029 to 1984, so does the 1991 film return and replicate its predecessor. Time is fixed, immutable and preordained, like a computer running and rerunning through its programming.

The thing is, though, in the Terminator world, time is not fixed. The apocalyptic future, in which the computer network Skynet attains sentience and destroys humanity in a nuclear apocalypse, is a possible future, but not the only one. There is, as the film famously declares, “No Fate.”

So T2 replicates T1, but it also refutes it, or contradicts it. In T2 Sarah Connor is not a hapless waitress, unlucky in love; she’s a badass, muscled-up, one woman death squad, who turns pens into deadly weapons and cocks a shotgun with one arm when her other is disabled because she’s just that tough. The muscle-bound Arnold from the future may beat up punks for their clothes and wear sunglasses in T2 just as in the first installment, but this time he’s the good guy, while the pale skinny dude is the nightmare villain. And by the same token, the inevitable apocalypse, with children vanishing into the white atomic light, is maybe not so inevitable. Sarah dreams about nuclear death over and over, but because she acts on her dreams, they may not come true. The film becomes not purely repetition, and not purely sequel, but an alloy of both—a variation on a theme, in which the characters try to take that old memory chip and make it learn something new.

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T2 is of a post-Cold War historical moment when the future looked unusually bright: if Russia and the United States could find common ground, why not humans and killer cyborgs, too? The good guys in T2 are able to avert nuclear apocalypse in part because Gorbachev did so first. But even while T2 looks ahead to a shiny utopia, its heart stays with the rust-covered past. The liquid metal, future tech T-1000 played with chillingly malice by Robert Patrick is, after all, the bad guy. The hero, on the other hand, is Schwarzenegger, star of the first film, now reborn slightly more grizzled, slightly more worn down, with joints that grind and squeak.

The not especially subtle subtext here is that the original film, with its low budget, gritty charm, is the protagonist. The first bleak, mean-spirited Cold War Terminator, in which the hero dies and the heroine rides off alone into the apocalypse, fights gamely against the glossy, big-budget post-Cold War Hollywoodization of the second film, with its top drawer special effects and smarmy, spunky Hollywood kid hero (Edward Furlong’s John Connor.) T2 has a conventional happy ending of noble sacrifice and a brighter day ahead. But it gets there by having that old clunky Terminator blow a hole in the sleek new Terminator. The new is the old crushing the new. The happy ending is that the sad ending sinks victorious into the molten metal.

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T2 is the greatest sequel ever not because it’s better than the original Terminator, but because it oozes around that original, and makes it part of itself, even as it takes on a different form. Terminator: Genysis tried to do something similar last year and sunk into a bloated puddle of ill-conceived, misshapen nostalgia. For the most part, going back in time doesn’t work. All the more reason to celebrate Terminator 2 which, 25 years later, still strides, impossibly, forward and back, a future built of old parts, like every sequel, but better.