Mad Jack
Mad Jack was a figure connected to the fairy circle broken by the Fifteenth Doctor. One of the letters in the circle which Ruby Sunday read had the message, "Rest in peace, Mad Jack".
The locals at Y Pren Marw told played a prank on Ruby, describing a man who was an insane killer who had drank at their pub; Ifor Jones, a queer individual, said that he was the sort of person Mad Jack would kill. They claimed the fairy circle was binding his soul to rest in peace, and the circle's breaking had "unbound" Jack, with the Woman possibly being his herald. They later laughed the whole thing off and said that the conception of the rural Welsh as being connected to witchcraft was racist.
Roger ap Gwilliam had many jobs in his youth, leading to him gaining the nickname "Mad Jack" due to him being a jack of all trades. Ruby heard this anecdote on television during a date, and it brought to mind the story she heard earlier, as well as the Doctor warning her about ap Gwilliam years before. (TV: 73 Yards [+]Loading...["73 Yards (TV story)"]) However, Ruby would later experience evidence that ap Gwilliam's premiership was still part of history even after the timeline in which she and the Doctor had broken the circle was aborted. (TV: Empire of Death [+]Loading...["Empire of Death (TV story)"])