Kastarion

"Kastarion" was the name given by the Anglican Marines to their unseen foe during their war on Kastarion 3. As no marine had ever seen one, rumours spread among the marines of their true nature. Some believed that they hid in the fog, others that they hid in the mud. Ultimately, the Fifteenth Doctor revealed that Kasrarion 3 was an uninhabited world before the marines arrived there, and that their war was a product of an algorithm artificially maintaining the conflict. (TV: Boom ^[+]Loading...["Boom (TV story)"])