This character doesn’t appear in game. At all. Well, how are you supposed to make it appear you ask? As some of you might already know, you have to do some file editing to get this person appear. However, this character is referenced to in game so let’s take a look at that.
The River Person will randomly say things while you’re taking a ride. Some of the things are believed to be pointing to Gaster. Namely the line about “Beware of the man who speaks in hands” and “Beware of the man who came from the other world”.

The first quote could be referencing how the font that Gaster speaks in, Wing Dings, has hand symbols for some of the letters. Some people in the fandom like to think that Gaster speaks in sign language to other monsters since they probably wouldn’t understand Wing Dings. Speaking of Wing Dings, that’s what people usually think the W. D. in his name stand for. The second one could be referencing how Gaster seems outworldly and has a similar structure to the previous quote. It could also be referring to another totally unrelated character called So Sorry.

Sans possibly has some connection to Gaster as well. Unless you subscribe to the Sans is Ness theory (which in my honest opinion is stupid and reaching quite a bit), several of the items in his workshop could possibly point to Gaster. The unreadable blueprints could be written in Wing Dings, hence why you can’t read them. The broken machine could point to how Gaster was the former Royal Scientist before Alphys took over (and Sans’ possible scientific background). Another thing to point out is that the blasters that Sans blasts you with in the genocide-only fight against him are called “Gaster Blasters” which is more evidence towards a possible connection between Sans and Gaster.

Now for the things you can only access with file editing. Let’s talk about the Gaster followers first. In room 91 (somewhere in waterfall) a grey version of Monster Kid (note- not a Gaster follower) will appear if the fun value is greater than 90. They will talk about depressing stuff like not existing or stuff like that. I’m not sure how much of it is related to Gaster but they are similar to the actual Gaster followers so I guess there’s some similarities.



The first Gaster follower is found outside of elevator L3 in Hotland (all the gaster followers are outside an elevator in Hotland) when the fun value is at 62. It’s a grey version of that one person in the MTT Hotel licking a plant. They will say that Gaster created the Core and that he was the precursor of Alphys (hence why he’s believed to be the former Royal Scientist) but tragically one day fell his creation. Some people believe that the creation the follower is talking about is the Core.



The second Gaster follower is found outside of elevator R1 when the fun value is 61. They are a grey version of that one person buying donuts from Muffet only instead of a donut they have what they say to be a piece of Gaster in their hand. They say that Gaster was shattered across time and space, and after their last dialogue about them holding Gaster, they disappear. The other two Gaster followers only disappear after you leave the room.


The third and final follower is found outside elevator L2 when the fun value is 63. This follower’s sprite seems to be rather unique with it’s design not being a grey version of an existing NPC. It’s kinda like a plant I guess with a dropping head at the top with a face and a small lump or leaf or something in the middle. It’ll talk about how great and amazing Gaster was as a Royal Scientist but one day his experiment went wrong. Also, they say that it’s rude to talk about someone who’s listening so… Gaster knows all and he’s Big Brother #confirmed.

[img]http://vignette1.wikia.nocookie.net/undertale/images/0/0e/Spr_g_follower_3_0.png/revision/latest?cb=20151015030102>

Now for the several rooms that you can only access with file editing stuff. Let’s start with the room where a sprite that is widely believed to be Gaster can be found. In Waterfall, when you’re in room 268 when the fun value is 66 (I WONDER WHAT ALL THESE SIXES COULD MEAN HM) there will be a door at the top. When you enter it, you will be in room 269 and at the top there will be what’s believed to be Gaster. If you approach it then Gaster will be surprised and disappear.

There’s also room 272 which has this- thing in the middle of the room. If you try to talk to it it’ll say something in Wing Dings (redacted) which is something I guess. This could also possibly be Gaster but eh. If you leave the room you’re in a sound test where you can listen to Gaster’s theme among 3 other themes.

Room 264 has what is believed to be Lab Entry 17 in the true lab. The whole this is written in Wing Dings however, so here’s the translated version (credit to the Undertale Wikia because I can't Wing Dings)-
“ENTRY NUMBER SEVENTEEN
DANK DANKER YET DANKER DARK DARKER YET DARKER
THE DARKNESS KEEPS GROWING
THE SHADOWS CUTTING DEEPER
PHOTON READINGS NEGATIVE
THIS NEXT EXPERIMENT
SEEMS
VERY
VERY
INTERESTING
...
WHAT DO YOU TWO THINK"

The two people that Gaster are referring to has been speculated to either be Sans and Papyrus (it’s theorized that Gaster is related to Sans and Papyrus like a dad or something, because some people believe that all three are skeletons and all three have a unique typeface) or Sans and Alphys (because of both of them being related to science and both of them knowing each other. It’s hinted at in the true pacifist ending).

There’s also a few other rooms that Gaster is in, and other possible references, namely room 123, a stable, and a random phone call near the fishing pole in Snowdin, but I feel that those are fairly minor. There’s also a ton of theories that I haven’t mentioned on Gaster that you could search up if you’re still interested. After all, this is a character bio not a list of character theories, even if with a character like this it’s entire existence is kinda just a big theory.

List of appearances
Undertale (Steam/PC/Mac)

*Reading this post fills you with DETERMINATION.

Sorry for the old post, but W.D. gaster is just a very mysterious character that's very awesome. A lot of people just love very mysterious characters in games, and Undertale is no exception.

I wish Toby released an update or something that allows you to have an interaction with Gaster or something. I love Gaster so much and it saddens me that he is not and probably never will be in any official form from Toby.