10 Doctor Who Characters Who Can Never Die
8. Ashildr
Maisie Williams' Ashildr had one of the craziest character arcs we've ever seen in Doctor Who, going from ordinary Viking girl to one of the universe's last remaining life forms over the course of her Series 9 journey.
She started out on the pathway to eternal life by dying, falling while defending her village against the technologically-superior Mire. Fortunately for her, the Doctor's "everybody lives!" mantra is one he's determined to abide by, so he resurrects her by reprogramming a Mire repair kit to give it human compatibility.
Crucially though, this repair kit doesn't just resurrect Ashildr - it continually heals her, ensuring that her body can never succumb to injury or death.
The Doctor admits this may have been a mistake, and his fears prove warranted when Ashildr - now going by the name "Me" - almost allows Earth to be invaded by a race of fire-breathing lion people (it's Doctor Who, just go with it). Me then plays a role in Clara's death, as well as the Doctor's four billion-year stretch inside his confession dial, so yeah... "mistake" seems quite accurate.
The character was last seen alongside a recently-revived Clara Oswald, putting her immortality to good use by exploring the universe in a funky, American diner-themed TARDIS. What better way to spend eternity?