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Control was a long-lived being who was a member of Light’s survey of ancient Earth.
When Light became dormant after the survey’s conclusion, Control was locked away in the ship by the mission’s surveyor, Josiah Samuel Smith, who had seized power during this time. The ship then resided in the cellar of Gabriel Chase in Perivale.
Due to her isolation, she became confused and childish over the years, wanting to attain her freedom and aspiring to become a proper lady. When freed, she began to evolve and took on a human appearance. She destroyed one of Josiah’s husks, disrupting his evolutionary ladder and weakening him. She then took him as her prisoner.
She then left to travel the universe together with Redvers Fenn-Cooper and Nimrod, her job as Control was taken on by Josiah. (Ghost Light)
BEHIND THE SCENES
As Light was an Eternal (Divided Loyalties), Control may have been as well.
The name “Control” is actually a fairly highbrow pun. Where Smith served as the variable, she served literally as the control. Eventually, Control evolves much more rapidly than Smith himself had done. (Ghost Light)