In Doctor Who, Ashildr, daughter of Einarr, was a young woman who lived in a Viking village on Earth in the 9th century. Her village was visited by an aliens called the Mire who posed as the Norse god Odin, in a plot to harvest the strongest warriors. Ashildr had a vivid imagination, perfect for Mire hologram technology, which the Doctor used to dupe the Mire into surrendering. Unfortunately Ashildr was killed in the process. The Doctor then used Mire technology to bring her back to life, but it also made her immortal. Ashildr kept detailed diaries of her life because she had trouble remembering much of her past, including her name. She eventually began referring to herself as 'Me', and in the 18th century, 'Lady Me'. Later, Ashildr traveled with Clara in a second TARDIS stolen from Gallifrey. She was the last living being at the end of the universe.
Ashildr is a variant of the Norse name Åshild, which means 'god battle'. The name Hildr comes from a valkyrie, one of Odin's handmaidens, who chose who would survive a battle, much as the Doctor did by saving Ashildr. Ashildr does not appear in the Social Security Administration's name database.
