In 1492, Count Federico used the seer Hieronymous to "foretell" deaths that would bring him closer to this 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.
He 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 a Hieronymous transformed by Helix energy. (TV: The Masque of Mandragora)