Even in 2026, after Deltarune Chapters 3 and 4 landed in 2025, I still find myself opening Undertale just to stare at a hidden room in Waterfall. Why? Because W.D. Gaster remains the most deliciously unresolved mystery in Toby Fox's universe. He is the former Royal Scientist who, according to a few cryptic followers, was shattered across time and space. He may not even appear in the game at all. And yet, I cannot stop reading theories about him. So let me walk you through the ones that keep me up at night, from the most widely accepted to the most delightfully weird.

8. He Is the Mystery Man

In a tiny percentage of playthroughs, a hidden room in Waterfall spawns a warped skeleton in a black robe. He has a garish smile. If I try to interact with him, he vanishes without a word. The game files call this sprite Mystery Man, but most fans, including me, accept that this is Gaster. It is the closest thing we get to a physical appearance, and it is barely there. That is exactly why it works.

7. He Might Be the Blank Sprite

Room 272 is another hidden file room. Inside, an unknown NPC appears as a blank white outline. If I walk toward it, it shows a message in WingDings font that translates to [redacted]. WingDings is Gaster's font, so that alone is suspicious. Then, when I leave Room 272, I am taken to a Sound Test Room. One of the testable tracks is called Gaster's Theme. Two clues, one empty sprite, and suddenly I am convinced this blank outline is either Gaster or a piece of him.

6. He Is the Devil

The number 6 shows up around Gaster in the internal files. His stats are all sixes. To see the Mystery Man, I need a Fun Value of 66. Since 666 is the devil's number, some players argue Gaster is a Satanic figure. I do not fully buy it, because Undertale is a game about forgiveness and hope, but the creepiness is undeniable. Gaster feels like a glitch in the moral fabric of the Underground.

5. He Is Always Watching

With specific Fun Values, I can meet four of Gaster's followers in places like Hotland. Each one speaks in riddles about the scientist's fate. They say he was shattered across time and space. They also insist Gaster can hear them, even when no one else is visible. That line gives me chills every time. If his consciousness is scattered across time and space, then maybe the game files themselves are the time and space his followers mean. He is not in one room. He is everywhere and nowhere.

4. His Name Is WingDings

One of the most accepted theories is that W.D. stands for WingDings. It makes sense. Many Gaster-related messages use the WingDings font. The Mystery Man looks like a skeleton, and the other two skeleton characters, Sans and Papyrus, are named after fonts. Gaster's last name is also close to Aster, another font. So W.D. Gaster becomes WingDings Aster, or something like it. I love this theory because it turns his name into a clue, not just a label.

3. He Was the Wrong Number

In Snowdin, my phone can ring at random. The caller asks for someone whose name starts with G, then stops and says they must have the wrong number. They even sing a wrong number song. There are not many G names in Undertale. Gerson is one, but he is a turtle merchant. Some fans think the caller was trying to reach Gaster. It is a small moment, but it fits the pattern of Gaster being just out of reach, one digit away from the present.

2. He Worked With Sans

Sans has a workshop with blueprints covered in illegible markings. Those markings might be WingDings. In a Genocide run, Sans attacks with weapons the game files call Gaster Blasters. Papyrus mentions that Sans loves science. Sans also has a quantum physics book and talks about alternate timelines. Put it together, and I cannot help but think Sans and Gaster were colleagues, maybe even friends. The former Royal Scientist and the pun-loving skeleton who knows too much. That is a prequel I would play in a heartbeat.

1. He Is Toby Fox

This is the theory that breaks the fourth wall, and it is so Undertale. In the True Lab, Alphys writes numbered memos. Entry 17 is missing. In the game files, that entry exists in WingDings and describes a dark experiment. Gaster writes that he finds it VERY, VERY, INTERESTING. The day before Toby Fox released Deltarune, the Undertale Twitter account posted about an upcoming event and ended with those same words, formatted the same way. Since Toby Fox created the game, fans theorized that Gaster is another avatar for him. In 2026, after Deltarune Chapters 3 and 4 expanded the mystery, that idea feels even more possible. Gaster might be the author's hand, reaching into the story.

Why Gaster Still Matters

In 2026, I do not need Undertale to confirm Gaster. The lack of confirmation is the point. He is the man who speaks in hands, the scientist shattered across time and space, and the reason I still open old game files like they are cursed documents. Whether he is a skeleton, a devil, a font, or Toby Fox himself, Gaster belongs to the fans now. And honestly? I think he likes it that way. 💀