After the death of John II, Montferrat had been plunged into a crisis brought on by the quick succession of two young rulers, neither of whom had the necessary authority to deal with internal state of chaos.

By marrying, of his own will, a Milanese woman, the daughter of Leonardo Malaspina, margrave of Lunigiana, he was forced to cede Asti to Gian Galeazzo.

After the death of his first and second wives, he remarried Margaret of Savoy, daughter of Amadeus, Prince of Achaea, on 17 February 1403.

Theodore maintained possession of these places until 1413, when, despite several military expeditions,[1] finding the government of both his Piedmontese and Lombard dominions too difficult, he gave them up in exchange for a large sum.

Theodore is one of the major antagonists in Rafael Sabatini's 1926 novel Bellarion the Fortunate, wherein he is portrayed as being sly, untrustworthy, and overly ambitious, though a formidable opponent in war.

Sabatini's book alters history slightly by having Theodore as Regent, when he was in fact the reigning Marquis.