Federico

Count Federico of San Martino was the uncle of Duke Giuliano, and lusted after the duchy itself.

Biography
In 1492, Count Federico used the seer Hieronymous to "foretell" deaths that would bring him closer to his goal. Federico's plan was one death from succeeding. Had the Fourth Doctor and Sarah not arrived in San Martino, he likely would have been able to kill his nephew, the last remaining person in the line of succession ahead of him.

Federico was a relatively unpleasant individual — Giuliano called him "a tyrant" — who influenced others with fear and intimidation. The Doctor himself was ordered publicly beheaded by Federico.

Ultimately, however, Federico was killed by Hieronymous who had been transformed by Helix energy. (TV: The Masque of Mandragora)