Knock lover
The knock lover is a minor character in Undertale. They are an unnamed and unseen character who lives in a house in northern Snowdin Town.
The knock lover has a fascination with the protagonist's knocking, to the point where they refuse to answer the door just to have a chance to hear it again.
When the protagonist knocks on their door, the knock lover states how excited they are to hear a door knocking.
On the Genocide Route, knocking on the door yields no response from the knock lover.
A similar NPC makes an appearance in Deltarune. They reside in Hometown's apartment complex.