Brown Jenkin is a rat-like creature with a human-like face who is a familiar to the witch Keziah Mason.

Brown Jenkin is "a small white-fanged furry thing", "no larger than a good-sized rat", which for years haunts the witch house and the town of Arkham in general, "nuzzl[ing] people curiously in the black hours before dawn".

Witnesses said it had long hair and the shape of a rat, but that its sharp-toothed, bearded face was evilly human while its paws were like tiny human hands. It took messages betwixt old Keziah and the devil, and was nursed on the witch's blood, which it sucked like a vampire. Its voice was a kind of loathsome titter, and it could speak all languages.