Clarence DeMarco

Clarence DeMarco was a serial killer active in Victorian London.

Biography
Judging by his accent, DeMarco was likely one of the many Polish Jews that fled to London during the late 19th century to escape the pogroms of Tsarist Russia. In 1893, he was apprehended in London for murdering fourteen women and was sentenced to death. In the end, his life was spared because he helped Madame Vastra by giving her information related to the Doctor, which he knew thanks to his ability to hear the 'whispers of the universe', such as coordinates that led to Trenzalore and the phrase, "The Doctor has a secret he will take to the grave... and it is discovered."