Ashildr

Ashildr was a Viking girl encountered by the Twelfth Doctor and Clara Oswald.

Biography
She greeted the Viking warriors when they returned from their journey with the Doctor and Clara in chains. They then glimpsed the sight of Odin in the sky after the Doctor had been trying to convince them that he was actually Odin.

She was given half of the sonic sunglasses by a Viking. She unlocked Clara's chains with them, but together they were beamed up to the Mire spaceship, where they were confronted by Odin. Foolishly, Ashildr declared war on the Mire for what they had done to the warriors in her village. (TV: The Girl Who Died)