Fürst is a German word for a ruler as well as a princely title. Fürsten were, starting in the Middle Ages, members of the highest nobility who ruled over states of the Holy Roman Empire and later its former territories, below the ruling Kaiser (emperor) or König (king).
Fürst zu Putbus, arms with a mantle and Fürsten crown.
Prince of the Holy Roman Empire
Prince of the Holy Roman Empire was a title attributed to a hereditary ruler, nobleman or prelate recognised as such by the Holy Roman Emperor.
Grave of the Prince of the Holy Roman Empire Johann Siebenhirter (1420–1508) at the parish church in Millstatt, Austria