Time of Origin: Originated from an unknown planet in the distant past; died on Earth in 1882.
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One of The Doctor’s most unique adversaries, Light’s entire plan was based around destroying or freezing all life on Earth in its present state for no other reason than that he wanted to ensure that his life’s work wouldn’t become out of date.
Having come to Earth as an agent of an unspecified agency, Light spent centuries in the distant past cataloguing all of the species that existed on Earth before going to ‘sleep’ in his ship, leaving only a few specimens in storage such as the Neanderthal Nimrod. However, Light’s ‘control specimen’, a being that evolved with the environment to aid Light’s analysis, eventually escaped the ship in 1881, where he killed the owner of the house and took his place, posing as Josiah Samuel Smith, forcing the lady of the house and her daughter to act as his housekeeper and ward respectively (It was never specified if he brainwashed them, intimidated them, or mentally influenced them into acting in that manner).
The Seventh Doctor and Ace eventually came to the house of Gabriel Chase when The Doctor decided to investigate the house based on Ace’s story of it; she had burnt the house down when she was thirteen because she had sensed an aura of great evil in it. While visiting the house, The Doctor and Ace were puzzled by Nimrod’s existence so far after his time and the presence of explorer Redvers Fenn-Cooper, driven mad after witnessing a strange light in the house’s basement. While fighting a panic attack after learning where she was, Ace discovered the ship in the basement, while The Doctor discovered that Smith had a hypnotised police officer kept in stone as part of his collection of life forms.
Although Ace’s actions awakened something else in the ship, The Doctor continued to distrust Smith’s claims that the other thing in the ship was a monster, having already determined that Smith was part of the ship’s cargo rather than its captain. After Smith made a local reverend who dismissed Darwin’s theories regress to a monkey, The Doctor tried to gain help by awakening the police officer, but the officer’s methodical approach proved useless to The Doctor, forcing him to make contact with ‘Control’, the entity in the ship, and use her to contact the ship’s true master, Light (Although he admitted that he didn’t know what he was doing and acknowledged that he may have awoken something worse than Smith). As Light appeared as a glowing golden man, The Doctor determined that Light was on a mission to catalogue all life in the universe; Smith was Light’s survey agent, capable of evolving to mimic the native forms of life in any environment, and Control was linked to the Survey Agent to prevent it from evolving too far and breaking free of Light, but the system had broken down after Smith managed to escape as Light slept.
Having been awakened, Light was shocked to witness what Earth had become since he went to ‘sleep; he had spent centuries cataloguing all of the species that lived on Earth during his first visit before going into stasis, but now that he had awoken all of those species had evolved and grown into new forms of life. Faced with the prospect of rewriting his entire catalogue – after taking a maid apart just to ‘see how it worked’ and confirm his location as Earth -, Light instead resolved to destroy all life on Earth so that it couldn’t evolve again, reverting the policeman back to primordial soup and turning the former lady of the house and her daughter into statues to ensure that they couldn’t change any more. However, Ace and The Doctor managed to counter Smith’s influence by helping Control evolve past Smith’s current state of development, allowing Fenn-Cooper to escape Smith’s control as he broke Smith’s control in favour of Control.
When Light threatened to trigger the destruction of his ship to destroy Earth and preserve his catalogue, The Doctor informed Light that even he was changing and evolving as they spoke, proving this analogy by revealing how Nimrod and Control had evolved beyond his command. As The Doctor confronted him with the impossibility of completing his catalogue, Light seemingly dispersed his own essence, leaving the aura of evil that would inspire Ace to destroy the house when she came to it as a child in the future. With Light gone, the surviving residents of the house and the ship’s former crew – Nimrod, Control and Fenn-Cooper, with Smith as a servant – departed in Light’s vessel to continue working on his catalogue, recognising that they had moved on from Earth despite their affection for it.