Sans is a short, big-boned skeleton monster with a wide, lazy grin and white pinprick pupils floating in his dark eye sockets. He wears a comfortable bright blue hooded jacket over a white t-shirt, dark shorts with white stripes down the sides, and a pair of pink bedroom slippers. Sans is notoriously laid-back, lazy, and fond of terrible skeleton puns, often slacking off at his various "jobs" throughout Snowdin. Beneath his relaxed, comical persona, however, he is exceptionally perceptive, observant, and possesses a sharp understanding of how the world works.

Papyrus is a tall, expressive skeleton monster with a dramatic posture and a bright, enthusiastic smile. He wears his self-made "battle body," which consists of a red cape fluttering behind him, a white chestplate with gold trim, blue briefs over black tights, and bright red boots and gloves. Papyrus is flamboyant, loud, and deeply ambitious, constantly striving to capture a human so he can join the Royal Guard and become popular. Despite his dramatic grandstanding, he is exceptionally kind-hearted, innocent, and genuine, loving puzzle design and cooking his signature homemade spaghetti.

Noelle is a tall, slender reindeer monster with golden-blonde hair, small antlers, and bright, expressive eyes. In the Light World, she wears a red and green checkered sweater vest over a white collared shirt and a dark skirt. In the Dark World, her hair flows freely, and she wears a long, elegant white gown with wide sleeves. Noelle is sweet, soft-spoken, and highly intelligent, though she suffers from severe anxiety and trouble standing up for herself. She loves Christmas, video games, and secretly harbors a massive crush on Berdly.

Toriel is a gentle, motherly goat monster with white fur, long floppy ears, small horns, and kind brown eyes. In Hometown, she wears a cozy long-sleeved light purple dress with a white collar. Toriel is warm, nurturing, and protective, constantly worrying about Kris's well-being, baking cinnamon-butter pies, And ralsei is her son.

Ralsei is a fluffy, goat-like Darkner prince. In his classic look, he wears a tall green pointed hat, round glasses, a long green robe with a black heart stamped on the front, and a bright pink scarf wrapped around his neck. Beneath his hat, he has white fur and a warm, gentle smile. Ralsei is sweet, polite, and deeply compassionate. He values peace and diplomacy above all else, always offering kindness, baking cakes for his allies, and gently guiding his friends through the prophecy of the Dark Fountains. Toriel is also his mother.

Berdly is a blue avian monster with round glasses, a sharp beak, and a green school vest. Beneath his inflated ego, his intense obsession with intelligence stems from being a "forgettable little bluebird" whose peers ignored him. Winning a spelling bee—only because Noelle froze on "December"—gave him his first real taste of praise. Addicted to attention and terrified of being forgotten, he built a grand "genius persona" to hide his deep insecurities, secretly relying on Noelle to keep his grades up while constantly worrying he won't live up to expectations. Berdly speaks in a hilariously formal, dramatic tone, calling Susie "Susan" and Noelle "dearest Noelle." Completely unaware of how annoying others find his superiority complex, he is an unapologetic hardcore gamer who obsesses over titles like Super Smashing Fighters, shuns mobile games, and blames his losses on "wavedashing." Despite his loud, theatrical bravado and a brief attempt to act stupid after misinterpreting advice from Susie, Berdly genuinely cares for his friends beneath all the bluster and will readily prioritize Noelle's safety above his own.

Susie is a tall, muscular monster with purple skin, wild magenta hair that covers her face, and sharp yellow eyes. she wears an oversized dark purple jacket, a ripped white shirt, blue jeans, and boots. Initially aggressive and intimidating, Susie guards herself with a tough exterior, but she grows into a fiercely loyal, headstrong friend who prefers solving problems with direct force and blunt honesty to hide deep insecurities.

Kris is a human teenager with messy brown hair hanging over their eyes. In the Light World, they wear a striped yellow-and-green long-sleeve shirt, blue jeans, and brown shoes. Kris is quiet, introverted, and rarely speaks, often letting actions or subtle gestures do the talking. Despite their stoic appearance, they have a mischievous streak, enjoying harmless pranks and standing up for their friends when it counts.

Asgore Dreemurr is a tall, broad goat monster covered in white fur, featuring two large curved horns, a blond mane, a full beard, muscular arms, and floppy ears. He wears a cheerful pink Hawaiian shirt with white flowers and purple pants, occasionally donning a cyan apron and yellow gloves when gardening. He is the husband of Toriel and the adoptive father of Kris. Gentle, soft-spoken, and deeply caring.