Miller was the Commander of the Royal Guards.
In 1868, when the Assassin Evie Frye infiltrated the Tower of London to find Lucy Thorne, who was attempting to discover the Shroud of Eden, she freed Miller from his imprisonment by the Templars, who were posing as Royal Guards. As a token of his gratitude, he then ordered the authentic Royal Guards not to attack Evie, as she was fighting on their side.