What is the name of the rat-like familiar in "The Dreams in the Witch House"?

The rat-like familiar in “The Dreams in the Witch House” is Brown Jenkin.

Brown Jenkin serves the witch Keziah Mason and haunts the Witch House in Arkham. Lovecraft describes the creature as a small, furry, white-fanged being no larger than a good-sized rat, though it has disturbing supernatural abilities and associations with witchcraft.

Jenkin is more than an ordinary animal. It appears during Walter Gilman’s nightmares and helps draw him into Keziah Mason’s occult activities. The creature is eventually responsible for Gilman’s death, emerging from his chest in one of the story’s most grotesque scenes.

The name is easy to confuse with other Lovecraftian or fantasy characters. Red Hook is a Brooklyn setting associated with another Lovecraft story, while Grey Mouser belongs to Fritz Leiber’s fantasy fiction. Brown Jenkin is specifically Mason’s familiar in the 1933 story.