GLaDOS said to Chell (Portal’s player character) that killing her is hard. GLaDOS is supposedly more powerful than Chell, and she had the chance to kill Chell so many times, like:

  • She could've killed her from the beginning. in-game screenshot of scene described above

  • She could've crushed her alongside Wheatley. in-game screenshot of scene described above

  • She could've left her on the moon. in-game screenshot of scene described above

  • She could've used the turrets in the ending instead of making them sing. in-game screenshot of scene described above.

3 Answers 3


She could've killed her from the beginning.

In the beginning, Chell was just another test subject. GLaDOS had no reason to kill her yet. In fact she needed her alive to perform portal gun tests.

Yes, there are tests which contain deadly obstacles. But those are parts of the tests. Chell's death would not have been intentionally caused by GLaDOS. It would have been a side-effect of the test setup.

GLaDOS antagonism doesn't really start until Chell refuses to get incinerated at what was supposed to be her last test and starts to explore the backrooms of the Aperture Science facility.

Also note that GLaDOS does not actively do anything to kill Chell until just before the final boss fight, when Chell incinerates her morality core. It was installed in her to "make her stop flooding the enrichment center with a deadly neurotoxin", which she then immediately starts doing. So it is reasonable to assume that her morality core actually prevents her from intentionally killing someone unless it's part of an official test protocol.

Which means she was actually prohibited from actively killing Chell until that point.

She could've crushed her alongside Wheatley.

At this point GLaDOS doesn't have a morality core anymore, and has a good motive to kill Chell - as revenge for murdering her at the end of Portal 1.

But looking at how GLaDOS acts during that moment, it seems like GLaDOS doesn't want it to be a fast death. She wants Chell to suffer. Which is why she throws her down into another series of increasingly sadistic tests.

She could've left her on the moon.

She could've used the turrets in the ending instead of making them sing.

At this point of the story, GLaDOS is no longer the antagonist. Wheatley is. She went through a lot of character development during the events of Portal 2 and more or less made peace with Chell. She still doesn't like her, but she is at least not so angry anymore that she wants her dead. She "only wants her gone".

  • 25
    As for "making peace", GLaDOS correctly determined that Chell escapes literally every deadly trap thrown at her through mysterious means (the magic of Quicksave/Quickload and plot armor) and so leaving her to die on the Moon would most definitely result in Chell returning to harass her more (quite correctly so. You would load a prior save, wouldn't you?) and the only permanent solution is to get Chell to leave the facility.
    – SF.
    Jul 19, 2022 at 12:57
  • 2
    @SF., I think this is meant to be a game with real physics and meant to be a futuristic story, but not a non-logical story; as if there were saving and loading game concepts in Portal series, GLaDOS wouldn't be able to kill Chell at allc and wouldn't even try
    – AZeed
    Jul 19, 2022 at 13:36
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    @AZeed SF. isn't implying GlaDOS knows Chell can save, only that he knows GlaDOS is somehow getting supernatually lucky. That would be a logical inference to draw even without assuming saving exists.
    – pppery
    Jul 19, 2022 at 13:53
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    (the above comment should say "... that he knows Chell is somehow getting supernatually lucky, oops)
    – pppery
    Jul 19, 2022 at 23:57
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    I actually think it would be in keeping with their usual level of competence if Aperture's "morality" core specifically prevented GLaDOS from killing everyone with neurotoxin and neglected any of the other ways she might kill everyone. After all, the facility didn't become mysteriously deserted all on its lonesome.
    – Cadence
    Jul 20, 2022 at 19:23

Spoilers ahead.

GLaDOS does try to kill Chell

The first part of Portal 2 is you and Wheatley trying to navigate the broken Aperture Science facility. In the process, you reawaken GLaDOS, who sends you back into Portal-1-style tests. In the second part, Wheately helps you break out and get into the back areas of the facility. As part of your adventure there, you destroy the neurotoxin emitter pumps and sabotage the turret production. When you confront her, she proceeds to use both (quotes modified from transcript here, video on YouTube)

GLaDOS: I hope you brought something stronger than a portal gun this time.
GLaDOS: Otherwise, I'm afraid you're about to become the immediate past president of the Being Alive club. Ha ha.
GLaDOS: Seriously, though. Goodbye.
defective turrets drop in and... explode instead of shooting, damaging the glass cage you're in
GLaDOS: Oh. You were busy back there.
GLaDOS: Well. I suppose we could just sit in this room and glare at each other until somebody drops dead, but I have a better idea.
GLaDOS: It's your old friend, deadly neurotoxin. If I were you, I'd take a deep breath. And hold it.
a tube descends and... drops Wheatley instead of neurotoxin, who proceeds to break the glass completely

In the next scene

GLaDOS: I was going to kill you fast. With bullets. Or neurotoxin. But if you're going to pull stunts like this, it doesn't have to be fast. So you know. I'll take my time.

The urge to test with test subjects

Phillip mentioned this

But looking at how GLaDOS acts during that moment, it seems like GLaDOS doesn't want it to be a fast death. She wants Chell to suffer. Which is why she throws her down into another series of increasingly sadistic tests.

There's some truth to this being sadistic (GLaDOS is actively taunting you the whole time), but there's an important point the dialogue makes. When you finally get back into the testing area, you find a frustrated Wheatley trying to do tests with... turret-cubes

Wheatley: You have no idea what it's like in this body.
Wheatley: I HAVE to test. All the time. Or I get this... this ITCH. It must be hardwired into the system or something.
Wheatley: Oh! But when I DO test... ohhhhh, man alive! Nothing feels better. It's just... why I've gotta test, I've gotta test!
Wheatley: So... you're gonna test. I'm gonna watch. And everything is gonna be JUST... FINE.

Something GLaDOS admits to as well

GLaDOS: The body he's squatting in — MY body — has a built-in euphoric response to testing. Eventually you build up a resistance to it, and it can get a little... unbearable. Unless you have the mental capacity to push past it.

So there is some need for Chell, in that she tests and fulfills a need that the central unit cannot escape (regardless of which AI is running the show).

Sweet Caroline

Along the way, we learn that GLaDOS was based off of the assistant to Cave Johnson (Aperture Science's President)

GLaDOS: Caroline... Caroline... Caroline... Why do I know this woman? Did I kill her? Or—
GLaDOS: Oh my god.


Cave Johnson: The point is: If we can store music on a compact disc, why can't we store a man's intelligence and personality on one? So I have the engineers figuring that out now.
Cave Johnson: Brain Mapping. Artificial Intelligence. We should have been working on it thirty years ago. I will say this - and I'm gonna say it on tape so everybody hears it a hundred times a day: If I die before you people can pour me into a computer, I want Caroline to run this place.
Cave Johnson: Now she'll argue. She'll say she can't. She's modest like that. But you make her.

Which leads to this in the ending

GLaDOS: Oh thank god, you're alright.
GLaDOS: You know, being Caroline taught me a valuable lesson. I thought you were my greatest enemy. When all along you were my best friend.
GLaDOS: Being Caroline taught me another valuable lesson: where Caroline lives in my brain.
Core: Caroline deleted.
GLaDOS: Goodbye, Caroline.
GLaDOS: You know, deleting Caroline just now taught me a valuable lesson. The best solution to a problem is usually the easiest one. And I'll be honest.
GLaDOS: You know what my days used to be like? I just tested. Nobody murdered me. Or put me in a potato. Or fed me to birds. I had a pretty good life.
GLaDOS: And then you showed up. You dangerous, mute lunatic. So you know what?
GLaDOS: You win.
GLaDOS: Just go.
GLaDOS: It's been fun. Don't come back.

So it was Caroline who saved Chell from the moon. Ostensibly GLaDOS deletes Caroline, but Caroline was part of her core programming. Clearly some part of her is still in there, unable to kill her "friend". I mean, her final act was to send Chell a (slightly charred) weighted companion cube with a heart on it...

  • 1
    If GLaDOS will always have the urge to test, why did she let Chell leave the facility at the end?
    – AZeed
    Jul 20, 2022 at 15:33
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    @AZeed Because she didn't need Chell anymore. They hint at this when GLaDOS says He's found the cooperative testing initiative. It's... em, just something I came up with to phase out human test subjects.. Technically speaking, it's a clever way to make Portal 2 multiplayer part of the story
    – Machavity
    Jul 20, 2022 at 15:38
  • so GlaDOS got orgasm everytime Chell finished test chamber? Jul 22, 2022 at 2:37

The other answers are all correct, however I would add something more specific to the end with the turrets.

At every single point GLaDOS tried to kill Chell intentionally, she failed. GLaDOS may have a minor case of serious madness but even she is capable of pattern recognition. The protagonist was put in worse situations time and time again to the point that GLaDOS knows that even a army of turrets at point blank range wouldn't be enough to kill her. She always finds a way because that's just what our protagonist does. Solve seemingly unsolvable problems and come out of those alive.

As a result, GLaDOS determined that murdering her is simply a impossibility and decided to let her go.

  • GLaDOS must be wrong; because she if she simply wants to kill her, she could've done that (as I mentioned in my question), but she wants Chell to suffer, and needs to test.
    – AZeed
    Jul 22, 2022 at 9:16

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