Of the many ways that Undertale grabs its audience, none are so intriguing as the mystery of what happened to W.D. Gaster. Although the game is filled with well-rounded, unique, and lovable characters of all personality types, it's this former Royal Scientist who may or may not even appear in the game at all who has spawned the wildest fan theories.
Officially, Gaster is only represented by a handful of sentences spoken by other characters, including his four elusive followers who may appear at random to the player. His fate is described as him having "shattered across time and space" – a concept so intriguing it has set legions of fans to combing through the Undertale game files in search of evidence of his existence. What they found only served to further pique the fandom's collective curiosity, and spawned some truly brilliant fan theories. Here are a few of those theories, from the most widely accepted, to the most creative, about "the man who speaks in hands."
8 He Is The Mystery Man
In a very small percentage of playthroughs, a mysterious unnamed sprite will appear in a hidden room in Waterfall. The sprite looks like a warped skeleton dressed in a black robe and wearing a garish smile. If the player attempts to interact with him, he disappears without a word.
The game files name this sprite as "Mystery Man," but it is generally accepted by the Undertale fandom that this sprite is supposed to be W.D. Gaster.
7 He Might Be The Blank Sprite
Undertale's game files include several hidden rooms, and one of them, Room 272, contains an unknown NPC. This character is a blank sprite made up of just a white outline that appears when the player walks towards it.
While this sprite does not appear anywhere else in the game, it draws two connections to Gaster in Room 272. If the player engages with this empty sprite, they are offered a message in WingDings font that translates to read simply: * [redacted]. WingDings is generally a font that is associated with the mysteries around Gaster in the game. Once the player leaves Room 272, they are taken to a Sound Test Room, where one of the testable sound files is called: "Gaster's Theme." These two details suggest that the blank sprite is related to Gaster, or might even be the missing former Royal Scientist.
6 He Is The Devil
The number 6 is used in reference to Gaster in a number of the internal game files. Although Gaster doesn't appear in the game, his stats appear in the game file, and every stat is some number of sixes. Since 666 is thought of as the devil's number, this leads some players to guess that Gaster is somehow a representation of the devil.
There is another tie-in between multiple 6s and Gaster. At the beginning of the game, the player is assigned a random number, called the Fun Value. In order to view the Mystery Man NPC, which is generally thought to be Gaster, the player needs to have the randomly assigned Fun Value of 66. While a literal Satanic character doesn't seem right with Undertale's themes of forgiveness and hope, there is definitely something super creepy about the Gaster mystery that fits with this theory.
5 He Is Always Watching
If the player has specific Fun Values, they have a chance to encounter four of Gaster's followers, among other secrets in places like Hotland. Each one of these sprites will offer some cryptic clues about the fate of the scientist, including the fact that, as a result of his last experiment, he was "shattered across time and space." They are all careful to watch their words, insisting that Gaster can hear them, although there is no other visible character around.
Fans have naturally theorized that this means that pieces of Gaster's consciousness exist across time and space. The concept of Gaster certainly does exist as different pieces of information scattered across the game files, so the game itself might be what his followers refer to as "time and space."
4 His Name Is WingDings
One of the more accepted theories about Gaster is that his first initials stand for WingDings. This theory stems from the fact that many of the messages related to the mystery of Gaster are written in the WingDings font.
This theory gains further traction in connection with Gaster being the Mystery Man sprite. This sprite looks like a skeleton, and two other skeletons in the game are both named after fonts as well – Papyrus and Sans. Gaster's last name is also remarkably close to another font type: Aster. All these small clues make it likely that W.D. does in fact stand for Wing Dings.
3 He Was The Wrong Number
One of the best comic relief parts of Undertale is the cell phone that Toriel gives Frisk at the beginning of the game. There's a spot in Snowdin at which, by random chance, the player may receive a phone call. The person or monster on the other side of the call will begin to ask for someone with a name that starts with G, before cutting themselves off to say that they must have the wrong number. (And singing a delightful wrong number song as a goodbye.)
There are very few characters in Undetale with a name that begins with the letter G (Gerson, the old turtle merchant, is one of them). Some players have theorized that this person must be Gaster.
2 He Worked With Sans
Throughout the game, there are hints that Sans might have been working with the former Royal Scientist. Sans has his own workshop, where there are blueprints on his desk covered in illegible markings that might be the Wingdings font. If the player fights Sans in a Genocide run, the latter will attack using canon-like weapons called Gaster Blasters in the game files.
Papyrus mentions that his brother has an affinity for science multiple times. Sans also makes a number of references to alternate timelines during his battle and has a book on quantum physics. Having the same interests as W.D. Gaster, combined with the other clues, makes it likely that Sans and Gaster were at least well-acquainted.
1 He Is Toby Fox
This theory leaps the bounds of Undertale's game framework and lands in the real world, which is ironically extremely Undertale. It begins in the True Lab, where the player can read a number of memos, supposedly written by Alphys, detailing her experiments with Determination and monsters. The memos are numbered, and one of them is missing – entry number 17.
This entry is found in the game files and contains a message written in Wingdings font, ostensibly written by Gaster. It details a dark experiment, that Gaster writes he finds:
"VERY,
VERY,
INTERESTING."
The day before Toby Fox released Delta Rune (the follow-up game to Undertale), the Undertale Twitter account posted a message about an upcoming event, and finished the message with those same words, formatted the same way. Since Toby Fox is the sole creator of the game, this led to fans theorizing that Gaster might be another of his Undertale avatars.