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 such as Carson believed that they hid in - or were made of - the fog, others such as Mundy Flynn thought that they hid in the mud. Ultimately, the Fifteenth Doctor revealed that Kastarion 3 was an uninhabited world before the marines arrived there, and that their war was a product of the Villengard algorithm artificially maintaining the conflict to keep an acceptable casualty rate, after it was activated by the Marines' warning shots fired upon arrival to the planet. (TV: Boom ^[+]Loading...["Boom (TV story)"])