Thomas Grey, Marquess of Dorset, is Queen Elizabeth's eldest son from her first marriage to Sir John Grey. He is half-brother to Edward V, Richard Duke of York, and Princess Beth. Thomas shares his mother's deep resentment toward Edward IV, stemming from his father's death at Yorkist hands. His Woodville family ties position him against Richard III and the Yorkist regime.

After Edward IV's death, Thomas engages in political schemes to bolster his family's influence during Edward V's minority. When Richard III seizes power, he flees into sanctuary at Westminster Abbey with his mother and siblings. Thomas later emerges to support conspiracies against Richard III, including efforts to delegitimize Richard's claim, fueling the conflict between Woodville loyalists and Richard's supporters.

Thomas plays a direct role in events concerning the young princes, Edward V and Richard Duke of York. He supports or participates in confining them within the Tower of London, a measure aimed at safeguarding them that ultimately places them under Richard III's control, aligning with his family's goal to preserve their claim during the unstable succession.

His narrative intertwines with pivotal political tensions, including his family's feud with William Hastings, rooted in rivalries over mistresses and court influence. Thomas's presence adds to the intricate web of betrayals and rivalries defining the Wars of the Roses as depicted in the series.