Holy Roman Empire
The empire was dissolved on 6 August 1806, when the last Holy Roman Emperor Francis II (from 1804, Emperor Francis I of Austria) abdicated, following a military defeat by the French under Napoleon at Austerlitz (see Treaty of Pressburg). Napoleon reorganized much of the Empire into the Confederation of the Rhine, a French satellite. Francis' House of Habsburg-Lorraine survived the demise of the empire, continuing to reign as Emperors of Austria and Kings of Hungary until the Habsburg empire's final dissolution in 1918 in the aftermath of World War I.
Kaiser
The Holy Roman Emperors (962–1806) called themselves "Kaiser", combining the imperial title with that of "King of the Romans" (assumed by the designated heir before the imperial coronation); they saw their rule as a continuation of that of the Roman Emperors and used the title derived from the title "Caesar" to reflect their supposed heritage.
In 1806 the Holy Roman Empire was dissolved, but the title of Kaiser was retained by the House of Habsburg, the head of which, beginning in 1804, bore the title of Emperor (Kaiser) of Austria. After 1438, the Habsburgs had provided most of Holy Roman Emperors, so they saw themselves as legitimate heirs to the title they adopted. Despite Habsburg ambitions however, the Austrian Empire could no longer claim to rule over most of Germany, although they did rule over large areas of lands inhabited by non-Germans in addition to Austria. There were four Kaisers of the Austrian Empire who all belonged to the Habsburg dynasty.