Emperor
The first Austrian Emperor was the last Holy Roman Emperor Francis II. In the face of aggressions by Napoleon, Francis feared for the future of the Holy Roman Empire. He wished to maintain his and his family's Imperial status in the event that the Holy Roman Empire should be dissolved, as it indeed was in 1806 when an Austrian-led army suffered a humiliating defeat at the Battle of Austerlitz. After which, the victorious Napoleon proceeded to dismantle the old "Reich" by severing a good portion from the empire and turning it into a separate Confederation of the Rhine. With the size of his imperial realm significantly reduced, Francis II, "Holy Roman Emperor" became Francis I, "Emperor of Austria". The new imperial title may have sounded less prestigious than the old one, but Francis' dynasty continued to rule from Austria and a Habsburg monarch was still an emperor ("Kaiser"), and not just merely a king ("König"), in name.
List of Imperial Diet participants (1792)
The Holy Roman Empire was a highly decentralized state for most of its history, composed of hundreds of smaller states, most of which operated with some degree of independent sovereignty. Although in the earlier part of the Middle Ages, under the Salian and Hohenstaufen emperors, it was relatively centralized, as time went on the Emperor lost more and more power to the Princes. The membership of the Imperial Diet in 1792, late in the Empire's history but before the beginning of the French Revolutionary Wars, gives some insight as to the composition of the Holy Roman Empire at that time.