Reverend Thomas Smith was a Protestant priest and a supporter of the future Elizabeth I. He plotted to remove her elder half-sister Queen Mary I from power in January 1555. He was also one of Evelyn Smythe's distant ancestors.
Shortly after the the Sixth Doctor's arrival in London, it was revealed that Thomas was secretly married to Lady Sarah Whiteside, one of Queen Mary's ladies-in-waiting, who was pregnant with his child. Although the Queen disapproved of this, the Doctor changed her mind. Thomas discovered his child would be named John Smith, one of the Doctor's aliases. His son John Whiteside-Smith later became a prominent member of Queen Elizabeth's court and played a role in the defeat of the Spanish Armada in 1588. (AUDIO: The Marian Conspiracy)