Dame Discord

Dame Discord, real name Darla Danvers, is an Englishwoman of low birth who stole an old pearl ring when she was a child... and has worn it ever since. Any time she would be harmed, or any time she speaks the phrase "For Crown and Country", she's wrapped in seemingly indestructible armor (which also protects her head, despite not showing a helmet), granted the power of flight, and given a bow that shoots lightning bolts. Disarming or breaking the bow doesn't help: it vanishes a few feet from her and reforms in her hand.

She's the terror of Great Britain, who pops up seemingly at random to raid museums for ancient treasures... that are always found on the black market within a week. Few know what she's after.

What she tries to hide is that she can't maintain the armor for more than about an hour a day, and none of the skill shown in her super form is her own. The armor aims for her. The armor flies for her. She picks her targets. She picks where she wants to go... but none of the supernatural skill she shows is hers. It's all thanks to the pearl ring she wears...