A brief quote that sparked my question: 'the reign of Maximilian I (as king and co-ruler with is father Frederick III after 1486, as sole ruler from 1493, and as emperor from 1508 to 1519).' This quote suggests someone could be the king of the HRE and not the emperor. I have also heard of the title 'King of the Romans' used by rulers of the HRE, which again suggests one did not have to be an emperor to lead or rule the Empire. I was wondering if someone could explain this to me. How could someone be the king of the HRE and only later become the emperor? Was there any difference in power and responsibility compared to being king or emperor.
In a sense, it developed around 1000 A.D. that "Rex Romanorum" was the title that the electors confered on the elected, before that it was "Rex Germaniae" or even "Rex Francorum" - they meant East Francia.
Before Maximilian it was implied that the elected would have to get the pope to crown him to be emperor. In 1508, Maximilan got the pope, Julius II., to confer upon him that he could call himself "Elected Roman Emperor" without getting crowned by the pope. His greatson, Charles V. called himself "Elected Emperor" after his election and the pope concured in 1520. However, Charles still managed to get crowned in 1530 by the pope in person. His successors kept the "Elected Emperor" part and weren't crowned by the pope anymore.
The difference between a crowned and annoited Emperor and the "King of the Romans" was prestige; going to Rome and getting the Pope to crown the King of the Romans showed that he was quite powerfull. For example, from 1220 to 1312 there was no coronation.
Compare that to what happened to Sigismund, who had to wait 22 years to be crowned.
Most emperors before Maximilian (his father and the emperors before 1220) and most of his successors sought to have their son crowned "King of the Romans" to have a successor to be monarch without another election after their death.