The Mystery of W.D. Gaster

An Undertale Theory




It is time for THE mystery of Undertale: The elusive Dr Gaster and his story. While there are a ton of theories, fan art, and really amazing fan-made fights out there, the truth is far from discovered, but I aim to finally lift the fog surrounding this most cryptic figure and all of that based on the content of the game. Incidentally, I do not know where the idea came from that Gaster wears a turtleneck, but literally 90% of fan art depicts him like this. So sorry in advance, I found no evidence for a turtleneck, but what I did found was the truth about the doctor. Please look at the links at the bottom first so that everyone is on the same page.

With the last Undertale update came a ton of interesting facts about Gaster, but first and foremost the fact that he could now be encountered in the game without having to mess with the code. This means that this ‘Mystery Man’, as he is referred to, is now canon within the game and while the actual chance to encounter him is very slim, it exists. But one step at a time, what do we know of Gaster. From the Gaster Follower NPCs that are hidden away and not actually in the game, we learn that Gaster was the previous royal scientist, creator of the core, and unlucky to fall into his own creation. His life was thus cut short and he was erased from existence, one of them even claims to hold a piece of the scientist and this is one of the key facts to remember. The river person mentions among various other facts about the game a “man who speaks in hands” and this fits with a file that uses the Wing Ding font to write about entry 17 and a very interesting experiment. The Wing Ding font is not readable per se, as it must first be deciphered, but it includes, among other symbols, hands in various positions.


– This is one of the few references to Gaster that were actually in the vanilla game –

Sans is the next bit of knowledge we can gather about the doctor. In his secret workshop we can find photographs with people unknown to the protagonist and a poorly drawn picture of three people with the words “don’t forget” on the back. Additionally, Sans’ laser skull thingy is referred to as “Gaster Blaster” in the game files. Hidden away in the sound test files is a piece of music called  “Gaster’s Theme”. A very rare and random event can cause the player to receive a phone call in Snowdin and a someone asking for a ‘G’, but hanging up shortly afterwards. Attempting to name the fallen human “Gaster” will cause the game to restart. So we can definitely infer that Gaster is an entity that is/was in the world of Undertale or at least has significance in it and now it is time to slowly unravel his identity, since you have all seen him already, more than once even.


– The skulls are labeled as “Gaster Blaster” in the game’s files –

Let’s start from the beginning. Gaster is a royal scientist and works on the core, but also on the determination extraction machine, since this was contained in the true lab and since Alphys seems to have less knowledge and understanding of determination and the consequences an injection can cause, I deem it valid to say that she did not build this machine. So Gaster didn’t necessarily fall into the core, but rather into his determination extraction machine and consequently dissolved in the determination gathered. However, as Alphys experiments show, monsters cannot endure determination in even smaller quantities, much less being submerged (figuratively speaking of course) in it. Gaster’s experiments at the time must have been somewhat controversial, since he had followers, meaning people that still believed in his visions, therefore not everyone agreed with his experiments or methods used. After falling into his creation Gaster was torn apart and spread over time and space, which in Undertale means being spread across the code of the game in various stages of development. (Here is an article, why I believe Undertale to be literally the game and nothing beyond it: Undertale is real!). Based on this, time and space are relative terms that only work if applied to games. So far so good. But why do the Gaster’s followers not exist in the game we play? Simple, because it is another version of reality. From the photograph we know that Sans must have a link to Gaster (given his weapon name, his mentioning of reports about the time space continuum, Gaster talking about two other entities and their thoughts on the experiment in entry 17, and so on). Sans and Papyrus must have been the lab assistances of the good doctor, given his appearance as a somewhat skeletal figure (altered by his little accident, but still somewhat visible), his speaking in a font, and being named after it. Sans and Papyrus changed their reality after the doctor’s accident, possibly due to the fact that the people did not favor their presence given the controversial nature of their experiments. By changing realties, they both forgot everything that happened, except for Sans who kept a drawing and the message ‘don’t forget’, forcing his brain to remember the other reality.


– Although the dive into true determination might have messed up his looks a bit, Gaster still has the basic physique of a skeleton –

The shopkeeper in Snowdin mentions both of them simply showing up one day, almost as if they just appeared. Sans, by using the picture to remind himself, kept his vast knowledge, but possibly deemed it better for his brother to live a “normal life” and did not tell him of their past, but he still uses his knowledge to keep watch over the timelines and thus he can be well aware of the player’s saving and restarting. He mentions our reports, signaling that this was not his work alone, but that credit goes to someone else as well. A recently across time and space scattered doctor perhaps? But it would seem that Sans cannot actually travel across time, only space. His movements in the game do not follow logic according to our point of view, since he leaves the opposite way to where he next shows up, meaning space does not hold him captive, but time does. He can observe and recognize fluctuations within the timeline, but cannot alter them, thus his nihilistic attitude. He can see how everything will play out, but is unable to change it. This is why he cannot save Gaster from falling into his creation, he even mentions having given up to go back a long time ago in his fight. Immediately afterwards he states that the surface doesn’t appeal to him either. This has been wrongly interpreted as him originating from the surface, when he is actually referring to Asgore’s plan which does not appeal to him anymore. The knowledge that everything can be reset at any point with no warning and the knowledge of what happened to Gaster and a world that works without him (we’ll get to that) rob Sans of any real hope for the future. Nihilism is his response. By fighting the Genocide player he can draw out the inevitable trying to break his determination. I do not want to make any assumption about Sans’, Papyrus’, and Gaster’s relation (father, sons, brother etc.), but the fact that they are connected seems rather obvious (font name, knowledge, and appearance). Speaking of fonts, let’s take a look at that.


– Key word: “Our”. In general the fight against Sans reveals a lot of things –

The River Person mentions a man that speaks in hands. What does this mean? Two things: Gaster uses the Wing Ding font to speak and that he is mute. He uses sign language to communicate, indicated by the Wing Ding font that is literally made up of signs. This is the only way a game without actual voice acting can portray a mute character. His full name would thus be Wing Ding Gaster. Some theorists assume him to be actually called Wing Ding Aster, since Aster is another font, but one that is never actually seen or uttered. Therefore, I can only conclude a much simpler solution to this: Gaster is his last name. He is referred to as “Dr Gaster” and Wing Ding is his first name. Last names do exist in Undertale, supported by the name Asriel Dreemurr (just for clarification’s sake). But all of this still does not reveal his whereabouts to us. Fear not, we are now getting to the heart of the matter. This is Gaster:

maxresdefault (1)

– The truth about Gaster –

Confused? The dog did not eat the picture. This is Gaster, or rather a part of him. From one of the Gaster Followers we learn that pieces of him exist and can physically manifest. A big part of him happened to possess (or take the shape) of the Annoying Dog. While this might sound far-fetched at first, hear me out. I consider the mystery man sprite to be the body (or at least part of the body) of Gaster, however, not much more. There is little to no consciousness within him, hence his disappearing after being interacted with. Another part of his physical being is held by one of his followers. And a part is present within the dog. The dog is shown to possess seemingly game breaking abilities (going beyond the collision boundaries of the game, moving himself into your inventory, entering the battle with Papyrus and in it altering the game space). The dog seems to possess some of the abilities Gaster would have gained after being spread across the code: Power over the game. However, it is still a dog and it uses this power for nothing else than to mess around, stealing orbs and special attacks and so forth.


– That’s what dogs do: Fill up your inventory, absorb your legendary artifact, and leave the collision boundaries of the game –

Another part of Gaster went into or became the River Person. This is the knowledge Gaster has gained and amassed. Yet, all this knowledge is without context or memory. The River Person has no recollection about any of this and simply says these random bits of trivia that should be far beyond his knowledge, unless someone has vast knowledge over many different timelines. These are, however, completely useless to the River Person, he tells them like bits of trivia to break he silence, because he has no knowledge about what any of this actually means. The last piece of Gaster that can be found in the game (by tempering a bit) is an NPC named Goner Kid. He talks about a world where everything is the same, except oneself does not exist and that the thought scares him. This is certainly one of Gaster’s fears that took form or hold of this creature. And Gaster is pretty much in this position. The reality we play does not include him, yet everything functions the same way. A Gaster Follower even hints at Alphys possibly having the same fate as Gaster, implying some determinism in the role of the royal scientist. Another physical part of Gaster can be found in a room via digging through game files again. This time, he looks much less like a defined being, perhaps this is the rest (or at least most of it) that would, in the end, make up his body. The statement in Wing Dings simply reads “[REDACTED]”.


– Note that the follower knows of both Gaster and Alphys, meaning he retained his knowledge about the doctor –

So what does all of this lead up to? Well, simply put, in the timeline we are playing Gaster has become a paradox. This is a world where he does not exist, yet everything functions just fine. Furthermore, he cannot exist in this world. Every aspect of him that gets recognized as such disappears. His physical body (mystery man) vanishes after being interacted with accompanied by a high note). The follower that holds a piece of him disappears after he mentions that this is a part of Gaster, simply because a piece of Gaster cannot exist in this version of reality that you (the player) brought him into by tempering with the files. If the player enters his name as “Gaster” the game restarts, due to the fact that Gaster cannot exist in this realm. The parts of Gaster that do not disappear (River Person, Annoying Dog, Goner Kid) are not identified as part of him and therefore do not contradict this reality. People can remember him (Sans and the followers), but only via unconventional means, i.e. memory jogging drawings or save-file tampering. But where is the rest of him, his consciousness, if part of his emotions, powers, knowledge, and body are scattered across the game?


– Aside from being an important clue, this line kind of scares me… –

As one follower says “[…] it’s rude to talk about someone who is listening.” W.D. Gaster has been spread across the game’s code. Parts of him have been written into other beings (like the Dog or the River Person), the sprites of his body are in the game, yet not in the game itself. They exist, but at the same time they do not. And due to the fact that his being is scattered throughout the code, he is always watching, since the game is running and the code processed into a playable game. Therefore, his fear has come true. He is doomed to observing a world where everything works fine without him and with no means of interaction.

By including some of Gaster’s parts in the game via the last update, Toby has given more proof that Gaster is an actually concept within the game and not just an unfinished aspect. I would consider him to be “complete”, as complete as he can get in his current state. Gaster is present within the game in various forms. While I would really like an actual encounter with him, the mystery is what makes him all the more interesting. I had a lot of fun theorizing about the sad doctor and I hope you had fun reading. I look forward to any other opinions on the matter, since I claim no objective truth. Right now, this is my deduction of what happened to W.D. Gaster, Undertale’s greatest mystery.


Gaste pciture


Here are three links with all the NPCs and so forth:

Image sources in order of appearance:



4 thoughts on “The Mystery of W.D. Gaster

  1. You have a pretty sound theory. Despite disagreeing with a few details (such as the Annoying Dog canonically representing Toby Fox), your assumptions were logical and interesting. There are two things you might need to know about, though. 1.) When Sans falls asleep in the genocide run, his ‘Z’s are in Aster font. 2.) There is an ever-present feature in ‘most’ dialogue boxes in the game, the Aster-isk that begins and possibly “listens” to every conversation.

    Liked by 1 person

    • Thank you for your comment.
      1. I did know about this, though I am not sure what to make of it, to be perfectly honest. I know some claim the Aster font is also related to Gaster due to the name, but I cannot make sense of why it would appear when San’s is sleeping. This could imply that Gaster has a bit more control in his sleep, but it does not show this in the game. But it is an oddity for sure.
      2. Interesting! I did not think about that. This could very well be the intended purpose of the asterisk. I’d need to go back and check when it is present and possibly where it is not. Thank you for the insightful comment.


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