The title "Duke of Portugal" refers to a noble rank historically associated with the Portuguese nobility. It was often granted to members of the royal family or prominent nobles, signifying their high status and influence within the kingdom. The title has its roots in the medieval period when Portugal was establishing its identity as a nation. The title has been held by various individuals throughout history, including the famous Prince Henry the Navigator, who played a crucial role in the Age of Discoveries. Although the title is no longer in active use, it remains a significant part of Portugal's noble heritage and history.