Zoë Nightshade

Zoe Nightshade is the daughter of Atlas, a powerful titan. Once serving under him in a garden, she was sent into exile after helping Hercules defeat Atlas. Eventually, she joined Artemis's Huntresses, and became their head (under Artemis, of course). She then helped Percy Jackson & crew during their journey in The Titan's Curse, until she was eventually killed by her father at the end.

When she was still a nymph, she gave Hercules her hair-clip, which transformed into Anaklusmos, the sword Percy Jackson now wields.