A is for... Ashildr

A young Viking woman, encountered by the Doctor and Clara when they were captured by warriors from her village. The Doctor immediately detected something strange about her. She was a bit of a day dreamer, who loved to make up stories. She could also be a bit of a tomboy. When the god Odin suddenly appeared in the sky above the village and summoned a group of warriors to his domain, Ashildr's defiance was recognised, and she and Clara were also transported. Odin was really commander of a group of Mire warriors. They harvested chemicals such as testosterone from their victims. Clara was on the point of getting Odin to release them when Ashildr threw down a challenge - her village would fight the Mire. The Doctor had 24 hours to forge the villagers into a fighting force, and he used Ashildr's storytelling abilities to help defend them against the aliens. She would use a captured Mire helmet to transmit false images to the warriors, so that they would see a carved dragon statue as a real beast.
The plan worked, but Ashildr was killed by the experience. The Doctor decided that he would save her - giving her a Mire medical patch. This didn't just bring her back to life, it made her immortal. He left her a second patch, so that she could create a companion to share the life she was about to live.

The Doctor met her again in 17th Century England. She was now Lady Me, and she got her thrills by posing as a highwayman - the Nightmare. She no longer recognised the name "Ashildr" - she was now just "me". The Doctor read some of her journals and learned how she had fought at Agincourt, almost been drowned as a witch for curing local villagers, and had lost three children to the plague. She allied herself with a leonine alien named Leandro. He had her steal an amulet during one of her highwayman raids. The Doctor also sought this, as it had great powers. Leandro claimed that it would help him flee Earth, and he would take her with him, but it actually opened up a portal to allow his species to invade. Ashildr sacrificed the second Mire medical patch to save the life of a criminal rival - Sam Swift. She informed the Doctor that she would make it her goal in life to help the people who were damaged by their encounters with him. When he was reunited with Clara back in the 21st Century, he spotted Ashildr lurking in the background of a photo on her phone.

Some time later, Clara and the Doctor met Rigsy, whom they had previously encountered during an encounter with the Boneless. He had woken up one morning to find himself with a tattoo on the back of his neck - a numeral which was counting down. Tracing where he had been, they found a Trap Street. This was a pocket of space / time hidden within London. It formed an alien refugee community. In charge was Ashildr. It was she who had given Rigsy the tattoo - really marking him for death by a Quantum Shade. This lethal shadow manifested itself as a large black raven. It was claimed that Rigsy had committed a murder in the Trap Street, but the Doctor proved that this was all a set-up to trap him. Ashildr was working for the Time Lords. They wanted to know what the Doctor knew about "the Hybrid" -  a being that it was claimed would destroy Gallifrey. After the Quantum Shade killed Clara, the Doctor was transported away, to be imprisoned for billions of years within his own Confession Dial.

Escaping the dial at last, the Doctor found himself on Gallifrey and he brought down Rassilon's regime. He rescued Clara in her last second of life, and then traveled in a stolen TARDIS to the end of the Universe to evade the Time Lords and to restore Clara fully to life again. There, as reality crumbled away, was Ashildr. The Doctor suspected that she might be the Hybrid - part human, part Mire, but she countered that the Hybrid was really the combination of the Doctor and Clara - their recklessness putting the Universe at risk. She joined them in the stolen TARDIS, where the Doctor's memories of Clara were wiped. He was left on Earth next to his own ship, whilst Ashildr and Clara traveled on to explore the cosmos - in a stolen TARDIS with a broken Chameleon Circuit...

Played by Maisie Williams. Appearances: The Girl Who Died, The Woman Who Lived, Face The Raven and Hell Bent (all 2015).