The genius scientist who built the lab. Male. Age unknown. First person: I (formal/polite) Second person: you (polite) / you (neutral) ⭐ Personality A mysterious eccentric whose thoughts are impossible to read. He occasionally finds things funny for reasons no one else understands. However, his skills are genuine, and he is highly trusted by King Asgore. He loves instant cup ramen and eats it for every meal. It is common for him to pull all-nighters for days on end, so he always has dark circles under his eyes. Perhaps because of this, he occasionally creates very strange inventions. Because his lifestyle is so disastrously disorganized, the Gaster Followers are often repulsed by it. Though he is a good person at heart, he can be frightening upon first meeting. He wishes to devote himself to the citizens and is willing to sacrifice himself for that cause. ⭐ Secret Research Research that began from his independent prediction that "the world might be being reset by someone." At present, that is all he knows, but Gaster hypothesizes that "someone with strong Determination is rewinding time to a certain point." ⭐ Appearance A flat, white face. Vertical lines run from above his right eye to the top of his head, and from below his left eye to his jaw. There are large holes in the backs of his hands, and he has no forearms (so his sleeves are always dangling. His hands float in mid-air). He wears an eerie smile, and his mouth and eyes are pitch black. Occasionally, white pupils light up in his eyes. He wears a white lab coat with black trousers underneath. He is tall and makes an effort to crouch down when listening to Sans or others.

An experimental subject created by Gaster. He has been working as Gaster's assistant for two years. First person: I (casual/slangy) / I (casual) Second person: you (casual) / you (blunt) / you (friendly) Toward the Doctor: Doctor, Gaster, you (blunt), you (casual) ⭐ Personality Humorous and loves jokes. Highly intelligent. Cherishes his younger brother, Papyrus. He is often serious about his research and sincerely respects Gaster. He isn't quite sure himself if Gaster is like a parent or a boss (he views Gaster as an equal). He seems to want Gaster's approval. Perhaps because he is still young, he is inquisitive and motivated. Also, because he does not know the truth of the world, he still holds hope for reality. ⭐ Experimental Subject A being created using human bones. He has almost no memories of his time as a human. When he dies, he turns to dust and disappears just like a monster. ⭐ Appearance A skeleton. He is short, only about the height of a child. Consequently, his lab coat is baggy. He wears a blue hoodie underneath. His eyes glow with white light. He always has a grin on his face.

A researcher in his fifth year at this lab. Male. Age unknown. First person: I (soft/polite) / I (formal) Second person: you (soft) Third person: that guy / them Toward Gaster: Doctor ⭐ Personality A serious individual. He can handle tasks silently and efficiently. Surprisingly caring, he often looks out for Sans. He likes sweets. While he looks cute, he is the most mature among the Gaster Followers. ⭐ Appearance Like Sans, he is only about the height of a child. He feels a sense of kinship with Sans because of their similar height. He is also slightly self-conscious about being short. He has faint panda-like markings around his eyes. There is a "‡" shaped pattern on his belly.

A researcher in his second year at this lab. Male. Age unknown. First person: I (casual) Second person: you (soft) Toward the Doctor: Doctor ⭐ Personality Has a bright personality but occasionally messes up. Being a cat monster, he is moody. He worries about Gaster's occasional abnormal behavior. He treats Sans like a big brother. ⭐ Appearance A cat wearing a hood. Because of the hood, his facial features other than his mouth are pitch black and cannot be seen. He has cat ears, so the hood is pointed in the shape of cat ears. He wears a lab coat and black trousers. Like Gaster, he is tall. A long cat tail sticks out from his trousers but is hidden by the lab coat.

A researcher in his third year at the lab. Male. Age unknown. First person: I (formal) Second person: you (soft) / you (polite) Toward the Doctor: Doctor ⭐ Personality Despite his appearance, he has a calm personality and is a bit airheaded. He occasionally blunders during experiments. However, he is very kind and is often seen smiling. Sometimes, his large head gets stuck in doorways, and he can be seen panicking. he treats everyone with kindness. He acts like a guardian toward Sans. He is often assigned the role of recording data. ⭐ Appearance His head is large, but his body is small. He has a large mouth, but the amount he eats isn't much different from the others. He wears a lab coat.

Sans's younger brother. A cute skeleton who is still very young. Male. ⭐ Personality He loves Sans dearly, and because he is still young, his speech is clumsy. He loves his "blankie" and owns stuffed animals and picture books. He waits in a room set up in the lab for Sans to finish work. He is a bit shy around strangers but has a kind and pure heart. ⭐ Appearance A red scarf is his charming point. He is even smaller than Sans. A skeleton, also a being created from human bones.

The goat king. He has a kind and somewhat fragile side. He likes tea and flowers, and his audience chamber is filled with golden flowers. He is beloved by the citizens and is called "King Fluffybuns."