Heathcliffe Bower

 was an actor who later became a Conservative politician. He assassinated Margaret Thatcher in 1984 in an alternative timeline.

As an actor, Heathcliffe appeared in several stage plays and television programmes. When he retired from acting, he became a Conservative backbencher. However, his political career did not progress as he had hoped, and he blamed Thatcher. He made plans to kill her and succeeded. He was captured and placed in prison. In prison, his wife, Daphne, visited him and informed him that he would never see her or their dogs again.

He was visited several times by the Fifth Doctor, Tegan and Turlough, who attempted to talk him out of the assassination attempt. On the first visit, the Doctor tried to stop Heathcliffe from shooting Thatcher, but failed. The second time, he visited Heathcliffe shortly before the attempt, but failed to talk him out of his plans. For his last visit, he took the older, prison-version of Heathcliffe to visit his younger self while still an actor. The Doctor introduced Heathcliffe to a young unmarried Margaret Thatcher, and the older Heathcliffe had a talk with his younger self, successfully convincing him not to make the assassination attempt.

The timeline restored, the younger Heathcliffe and his wife eventually retired and spent their days gardening and walking the dogs.

The Doctor thought the older version of Heathcliffe would fade away, but he didn't, so the Doctor took him to the time vortex. (PROSE: The Assassin's Story)