Odin (The Girl Who Died)

"Odin" was a leader of a species called the Mire, a warrior race from the future. He took upon himself a hologram projection to appear human and adopted the name of Odin to trick Viking villagers by choosing them for the halls of Valhalla, in fact a place to kill them, to feed off of them.

Biography
He appeared in a cloud to the Viking villagers by use of a hologram, telling them to send their best warriors to dine with him in Valhalla. When his henchmen were sent down, they selected the strongest warriors and brought them up to their spaceship, where they were all killed except for Ashildr and Clara Oswald, who had brought half of the sonic sunglasses with them.