Sir Theodore is the captain of the king's Guard and has lead numerous battles mentioned throughout the series.
Jane is his squire and he teaches her how to fight and important lessons that a knight will need in battle. Wise, fair and serious, Sir Theodore acts as a father figure to Jane. Although he may come across as stern and earnest, he does have a kindly and compassionate side and a sense of humour, as shown by his love of All Fool's Day.