Title: Holy Roman Empire
Content:   A prospective Emperor first had to be elected King of the Romans (Latin: Rex Romanorum; German: römischer König). German kings had been elected since the 9th century; at that point they were chosen by the leaders of the five most important tribes (the Salian Franks of Lorraine, Ripuarian Franks of Franconia, Saxons, Bavarians, and Swabians). In the Holy Roman Empire, the main dukes and bishops of the kingdom elected the King of the Romans. In 1356, Emperor Charles IV issued the Golden Bull, which limited the electors to seven: the King of Bohemia, the Count Palatine of the Rhine, the Duke of Saxony, the Margrave of Brandenburg, and the archbishops of Cologne, Mainz, and Trier. During the Thirty Years' War, the 
Title: Holy Roman Emperor
Content:  Berthold V, Duke of Zähringen, establishes the election procedure by (unnamed) princes of the realm, reserving for the pope the right to approve of the candidates. A letter of Pope Urban IV (1263), in the context of the disputed vote of 1256 and the subsequent interregnum, suggests that by "immemorial custom", seven princes had the right to elect the king and future emperor. The seven prince-electors are named in the Golden Bull of 1356: the archbishop of Mainz, the archbishop of Trier, the archbishop of Cologne, the king of Bohemia, the count palatine of the Rhine, the duke of Saxony and the margrave of Brandenburg. After 1438, the kings remained in the house of Habsburg and Habsburg-Lorraine, with the brief exception of Charles VII, who was a Wittelsbach. 
Title: Kingdom of Germany
Content:  the Holy Empire. This idea was met with horror in Germany. When Rudolf I was elected, the emotional attachment the German people had with the superior dignity of the universalistic Roman title had become so firmly established that it was unacceptable to separate the German kingship from it. There was a strong reluctance by the Emperors to use "German" titles due to strong attachment to Roman symbolism, and it seemed to be actively avoided. References to "German" titles were less rare but still uncommon among vassals and chroniclers. From 1250 onward, the association between "Germans" and the whole Empire became stronger. As post-Staufer German monarchs were too 
Title: Holy Roman Empire
Content:  himself. Later Emperors dispensed with the papal coronation altogether, being content with the styling Emperor-Elect: the last Emperor to be crowned by the Pope was Charles V in 1530. The Emperor had to be male and of noble blood. No law required him to be a Catholic, but as the majority of the Electors adhered to this faith, no Protestant was ever elected. Whether and to what degree he had to be German was disputed among the Electors, contemporary experts in constitutional law, and the public. During the Middle Ages, some Kings and Emperors were not of German origin, but since the Renaissance, German heritage was regarded as vital for a candidate in order to be eligible for imperial office.
Title: King of the Romans
Content:  King of the Romans (Rex Romanorum; König der Römer) was the title used by the German king following his election by the princes from the reign of Henry II (1002–1024, emperor from 1014) onward. The title predominantly amounted to being the emperor of the Holy Roman Empire, a title long dependent upon coronation by the pope. The title originally referred to any elected German king who had not yet been granted the imperial regalia and title of emperor at the hands of the pope. Later, it came to be used solely for the heir-designate to the imperial throne between his election (during the lifetime of a sitting emperor) and his succession upon the death of the emperor. The title became functionally obsolete with the abolition of the requirement for emperors to be crowned by the pope in 1508 
Title: Holy Roman Emperor
Content:  There was no Holy Roman emperor between 924 and 962. While earlier Germanic and Italian monarchs had been crowned as Roman emperors, the actual Holy Roman Empire is usually considered to have begun with the crowning of the Saxon king Otto I. It was officially an elective position, though at times it ran in families, notably the four generations of the Salian dynasty in the 11th century. From the end of the Salian dynasty through the middle 15th century, the emperors drew from many different German dynasties, and it was rare for the throne to pass from father to son. That changed with the ascension of the Austrian House of Habsburg, as an unbroken line of Habsburgs held the imperial throne until the 18th century. Later a cadet branch known as the House of Habsburg-Lorraine passed it from father to son until the abolition of the Empire in 1806. Notably, the Habsburgs dispensed with the requirement that emperors be crowned by the pope before exercising their office. Starting with Ferdinand I, all successive emperors forwent the traditional coronation.
Title: Holy Roman Empire
Content:  When the Salian dynasty ended with Henry V's death in 1125, the princes chose not to elect the next of kin, but rather Lothair, the moderately powerful but already old Duke of Saxony. When he died in 1137, the princes again aimed to check royal power; accordingly they did not elect Lothair's favoured heir, his son-in-law Henry the Proud of the Welf family, but Conrad III of the Hohenstaufen family, the grandson of Emperor Henry IV and thus a nephew of Emperor Henry V. This led to over a century of strife between the two houses. Conrad ousted the Welfs from 
Title: List of German monarchs
Content:  The title "King of the Romans", used in the Holy Roman Empire, was, from the coronation of Henry II, considered equivalent to King of Germany. A king was chosen by the German electors and would then proceed to Rome to be crowned emperor by the pope.
Title: Holy Roman Empire
Content:  regnum ("the whole kingdom", as opposed to the regional kingdoms), imperium christianum ("Christian empire"), or Romanum imperium ("Roman empire"), but the Emperor's legitimacy always rested on the concept of translatio imperii, that he held supreme power inherited from the ancient emperors of Rome. The dynastic office of Holy Roman Emperor was traditionally elective through the mostly German prince-electors, the highest-ranking noblemen of the empire; they would elect one of their peers as "King of the Romans" to be crowned emperor by the Pope, although the tradition of papal coronations was discontinued in the 16th century. The empire never achieved the extent of political unification as was formed to the 
Title: Princes of the Holy Roman Empire
Content:   Prince of the Holy Roman Empire (princeps imperii, Reichsfürst, cf. Fürst) was a title attributed to a hereditary ruler, nobleman or prelate recognised as such by the Holy Roman Emperor.

Question: the german princes who chose the holy roman empire were called?
Answer: prince-electors.
the Prince-Electors.