The homunculus who aided in searching for Assassin of “Black.” After the war, she went with Caules to London. She actually appears stealthily in one of the illustrations of Volume 3, instead of Tool.
The homunculi created by Gordes have somewhat varied personalities and abilities, and Althea is a model that excels in magecraft. Her personality is exactly like that of a homunculus: reserved, yet wicked tongued. In London, she basically helps with household chores… She is also responsible for helping with Caules’ magecraft, but she has taken up a part-time job searching for familiars with magecraft.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia