Bonea

Harry Dresden's Parasite is first mentioned in Cold Days. It first appears in Skin Game.

Cold Days
In Cold Days, the parasite is mentioned by Demonreach's genius loci as keeping Harry alive and metabolically active.

Skin Game
In Skin Game, the parasite is used by Mab as a threat to coerce Harry in doing her bidding. The parasite is later revealed to be the creation of Lasciel's sacrifice for Harry, as "love is a type of creation." The spirit has features from Elaine Mallory, Susan Rodriguez, and Karrin Murphy. The spirit has grown immensely since its creation, and has to escape Dresden's head in order to keep growing. Mab's earring cause the spirit to turn into stone. The spirit is "delivered" into the skull Dresden makes for Bob (???).