Former king of the monsters, he was the one who declared war on humanity, just like in the original game.
However, he was unable to commit to his plan, and after the first SOUL was taken, retreated to the Ruins to atone.
Hides his burdens under a smile and focuses on improving life within the Ruins wherever he can. He’s planted gardens. He’s left his home open to any visitors, hosting weekly tea gatherings, and even softened the more dangerous puzzles by removing spikes and adding pillows to cushion the pitfalls.
Is very close to Napstablook, having assisted them with their self-esteem issues and often lets them stay in the guest bedroom in his house.
Is a father figure to Papyrus and later Frisk. He’s known Papyrus for many years and has shared his knowledge of plants with him, while Papyrus has shared his enthusiasm for puzzles and cooking.
Does not begrudge Toriel in the slightest, feeling as though the more hopeless state of the Underground is his fault and that she’s the more deserving ruler.
He’s much more hands off with Frisk during their time in the Ruins, allowing them to explore and discover on their own. He only grows more protective after an incident involving three hostile monsters.
Only keeps the Ruins door closed to keep out the cold and to protect the privacy of those who live there. In truth, he welcomes visitors with open arms.