Frederick Barbarossa, also known as Frederick I, was the Holy Roman Emperor from 1155 until his death 35 years later. He was elected King of Germany in Frankfurt on 4 March 1152 and crowned in Aachen on 9 March 1152. Historians consider him among the Holy Roman Empire's greatest medieval emperors. He combined qualities that made him appear almost superhuman to his contemporaries: his longevity, his ambition, his extraordinary skills at organization, his battlefield acumen and his political perspicacity. His contributions to Central European society and culture include the reestablishment of the Corpus Juris Civilis, or the Roman rule of law, which counterbalanced the papal power that dominated the German states since the conclusion of the Investiture controversy.

During Frederick's long stays in Italy, the German princes became stronger and began a successful colonization of Slavic lands. Offers of reduced taxes and manorial duties enticed many Germans to settle in the east in the course of the Ostsiedlung. In 1163 Frederick waged a successful campaign against the Kingdom of Poland in order to re-install the Silesian dukes of the Piast dynasty. With the German colonization, the Empire increased in size and came to include the Duchy of Pomerania. A quickening economic life in Germany increased the number of towns and Imperial cities, and gave them greater importance. It was also during this period that castles and courts replaced monasteries as centers of culture.

From 1165 on, Frederick pursued economic policies to encourage growth and trade. There is no question that his reign was a period of major economic growth in Germany, but it is impossible now to determine how much of that growth was owed to Frederick's policies. He died on route to the Holy Land during the Third Crusade.