Koth (The Twilight Kingdom)

 was a war hero, but became a terrorist. His family was killed in a pandemic, and the government atomised the area rather than risk the disease spreading. They didn't tell him that this happened and with no bodies to bury he turned against the state. The creature in the cave had used his body to feed itself so the real Koth couldn't move and what everyone had seen was a psychic imprint. (AUDIO: The Twilight Kingdom)