In all instances of "Doom", many people including marines have been zombified (in Doom3 drastically visualized by skull ghosts) or infected with a Lost Soul (granted, this one seems to prefer females).

For the leaders of Hell (or Betruger) it should be obvious: If this annoying guy with the gun cannot be taken out we should convert him. Why isn't he converted like the others ?

What is the in-game explanation (if there is one) that the hero resists infection ?

ADDENDUM: I think barbecue explained it well for Doom I/II and Tim B for Doom 3, the infection really changed. Would have given correct answer for both of them if possible, but because I referred to Doom in the title, I accepted barbecues answer.

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    Should I worry that after all these years simply reading this question made me recall all the levels (which I still remember from muscle memory in some cases...), and worse than that, gave me the itch to play it again?
    – Francesco
    Commented Sep 21, 2015 at 9:38
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    @Francesco I am very, very sorry to trigger that. If it is too severe, please think about joining Doomplayers Anonymous. Commented Sep 21, 2015 at 9:42
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    The answer to this seems to be very obvious. The protagonist doesn't die, therefore he doesn't turn into a zombie. Commented Sep 21, 2015 at 11:46
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    If you're asking a question about story, you utterly missed the point of Doom... Commented Sep 21, 2015 at 15:36
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    @R.. No joke: The plot may be simple and mundane, but if we take the standard Hollywood sci-fi flick and the majority of sci-fi books as benchmark, Doom's story is shockingly realistic, consistent and developed. We are confronted every day here with much, much harder stuff to swallow...do you know Doctor Who's moon spider ? Commented Sep 21, 2015 at 22:14

4 Answers 4


The in-game explanation is extremely limited, consisting of a brief synopsis of the plot in the manual, but I believe it is sufficient.

You and your buddies, the only combat troop for fifty million miles were sent up pronto to Phobos. You were ordered to secure the perimeter of the base while the rest of the team went inside. For several hours, your radio picked up the sounds of combat: guns firing, men yelling orders, screams, bones cracking, then finally, silence. Seems your buddies are dead.

Doomguy's companions preceding him into the complex have all been killed. But he then encounters them again, as undead monsters.

From an in-game perspective, the Doomguy doesn't become a zombie because he survives. As long as he stays alive and avoids capture, he won't become a monster. Once he dies. he will also become undead, but of course the player simply reloads.

Currently, the original Doom Readme.txt file can be found here. This is the documentation which was included with the shareware game.

  • I think they changed the infection from Doom I/II to Doom 3. In the old ones the zombies must have died before, in Doom 3 we have those skull ghost infection. So while it answers the original Doom game, the question is still open for Doom 3. Commented Sep 21, 2015 at 6:57
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    I don't think this is exactly right - there's plenty of dead marines around, wearing the same outfit you are. I always assumed those are your dead buddies. The undead you meet on your way would presumably be the original guards of the place (different look, different equipment, possibly a long exposure to the (spoiler alert) portals to Hell). It might simply be that it takes time - it's quite possible the original crew were exposed for months before the monsters from Hell came pouring in. Or, given the limited spaceship capability, it took you months to get there. Mars ain't exactly close.
    – Luaan
    Commented Sep 21, 2015 at 7:42
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    @Luaan Tim B's answer pointed that out and I think he and you nailed it. Commented Sep 21, 2015 at 8:50
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    @Luaan, the protagonist and other marines don't travel to Mars from Earth, they travel to Phobos from Mars. And the events unfold very quickly. 'A few hours ago, Mars received a garbled message from Phobos. "We require immediate military support. Something fraggin' evil is coming out of the Gateways! Computer systems have gone berserk!"'
    – barbecue
    Commented Sep 21, 2015 at 11:53
  • Good point - I forgot you didn't get there from Earth (got that mixed up with Doom II, I guess). However, the teleportation gates were on Phobos and Deimos, and probably operational for quite some time. The invasion might have happened after the hellish influence already poisioned the crews in the stations. And you run through the whole story in about an hour, so even the "few hours" of delay till you get there is significant. Not to mention the fact that you spend most of that in Hell...
    – Luaan
    Commented Sep 21, 2015 at 12:19

One thing to add to the other answers is that in Doom 3 you have literally just arrived. As you are traveling through the base if you listen to the recordings and read the reports you will see that people have been gradually going insane over time.

As a new arrival the effects of the portal have not yet had a chance to work on you. Additionally when the breach happened you were a long way from it, being outside of the base. These two factors combined to mean you survived the initial wave of infection.

After that maybe you would remain resistant, maybe not. It's not clear as the entire game takes place over a lower span than the days or weeks needed to infect the base and assuming you won the game you never died.

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    That makes sense. In the original Doom he was a long time with his buddies, but only dead are awakened as zombies. In Doom 3 he arrived together with Elliot Swann and Jack Campbell who died normally and uninfected. Commented Sep 21, 2015 at 8:48

I'll need to pull up the quotes, but from what I recall from both the books as well as the film (the latter isn't likely to be canon), the zombification is an infection, without airborne vector. In other words, to be infected, a zombie virus must be introduced to your body via contact/fluid exchange (e.g. a zombie biting you). In addition, the protagonist in the book speculates that this only happens once you die.

So, the protagonist isn't so much "immmune", as simply is never bitten (because the enemies shoot him, not bite - and when they try to bite, like in the book or film, they never manage to).

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    In Doom 3 a scientist and a marine are shown to be infected by skull ghosts without physical contact. There a cutscenes on youtube. And already transformed zombies do bite and scratch. Commented Sep 21, 2015 at 6:54
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    @ThorstenS. - they do (according to the book) but they never succeed to bite and scratch the protagonist Commented Sep 21, 2015 at 18:48

In the movie (so probably doesn't have anything to do with the games, but still might merit an answer) the main dude IS infected.

How they explained it in the movie is that when humans are injected with a gene altering substance it is supposed to make you super human, however it brings out the best/worst in you, kind of like in captain america, however, if it brings out the worst in you, you turn into a zombie creature thing.

Near the end the main dude takes a chance and gets injected with the substance and becomes superhuman and is able to contain the outbreak.

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