Althea Duchannes is a member of the Duchannes family, the sister of Emmaline Duchannes and Sarafine and Delphine's aunt thus being Lena and Ridley Duchannes' great-aunt. She was a Dark Evo, meaning she can shift into anyone she wanted and can also control the minds of others and make mortals do whatever she wants, like a Siren.
When she turned sixteen and was Claimed by the Dark, her mother couldn't stand to send her away, and tried to keep her daughter with her, but eventually she was forced to after a boy disappeared and it became obvious that there was no turning back. Since then, they can't live with their parents until they're Claimed.
As an Evo, she is an incredibly powerful Caster. She can control someone and influence them to do whatever she wants, like a Siren, and can morph and sound like anyone she wants. Also being an Evo, an extremely powerful Caster, she has the ability to Kelt and borrow the powers of any Caster she touches.