Duke Giuliano of San Martino was the nephew of Count Federico. He became the lawful heir to the duchy after his father died in 1492, but his accession was actively contested by his uncle. Indeed, he was the target of his uncle's murderous ambitions, and became the victim of Federico's numerous attempts on his life and reputation.
A man of science and liberal thought — quite literally a "Renaissance man" — he was naturally inclined to trust the Fourth Doctor despite Federico's attempts to label the Doctor as a "spy" and a "sorcerer". The two struck up a friendship once the Doctor began to apply scientific reason to explain the mystery of guards whose bodies had been desiccated by the Mandragora Helix. This bond was strengthened further when the Doctor joined Giuliano in an out-numbered sword fight against Federico's men.
He was loyally assisted by his companion, Marco. He tended to be more temperate than his friend, however. For instance, when Captain Rossini — a man responsible for many of the deaths ordered by Federico — laid down his arms, Marco argued for his death. Giuliano instead required Rossini jailed while an appropriate course of action was considered.
After the cult's defeat, Duke Giuliano organised the survivors of the Brotherhood of Demnos into a beneficent group known as the Orbus Postramo. (AUDIO: Dreamland) His journal, the Book of Tomorrows describing his adventures with the Doctor, became their holy book. (AUDIO: Fatal Consequences)