Amaltheia

Amaltheia was a sacred goat of Zeus.

History
Rhea had Amaltheia nurse Zeus when she had hid him away from Kronos. Later, Zeus sacrificed her and used her hide to create Aegis.

The Diary of Luke Castellan
When Thalia was twelve, she ran away from home in Los Angeles and discovered Amaltheia. She followed her, seeing the goat as a sign from Zeus. She was lured to a dragon's cave where she met Luke Castellan. Later, Amaltheia would reappear in Richmond, Virginia, where she would lead Thalia and Luke to a mansion which held a treasure for Thalia, which turned out to be a deadly trap. But with the help of Luke, Thalia discovered Amaltheia had lead her to a gift from Zeus, Aegis, which she was able to use to battle the lecrotae and save Luke.