Clarence DeMarco
Clarence DeMarco was a Polish serial killer active in Victorian London.
In 1893, he was apprehended in London for murdering fourteen women and was sentenced to death.
The day before his execution, he was approached by the Whispermen and the coordinates to Trenzalore were impressed onto his memory. (HOMEVID: Clarence and the Whispermen)
In the end, his execution was postponed because he helped Madame Vastra by giving her information related to the Doctor, such as coordinates that led to Trenzalore and the phrase, "The Doctor has a secret, you know. He has one he will take to the grave... and it is discovered." (TV: The Name of the Doctor)
It is implied that he was spared from his execution as according to the Whispermen, he would live to a great age but always have a troubled sleep. (HOMEVID: Clarence and the Whispermen)
