Kaiser is the German title meaning "emperor". Like the Bulgarian, Serbian and Russian Tsar it is directly derived from the Roman emperors' title of Caesar, which in turn is derived from the personal name of a branch of the gens (clan) Julia, to which Gaius Julius Caesar, the forebear of the first imperial family, belonged. Although the British monarchs styled "Emperor of India" were also called "Kaisar-i-Hind" in Hindi and Urdu, this word, although ultimately sharing the same Latin origin, is derived from the Greek kaisar, not the German Kaiser.

In English, the term the Kaiser is usually reserved for the emperors of the German Empire, the emperors of the Austrian Empire and those of the Austro-Hungarian Empire. During the First World War, the term the Kaiser—especially as applied to Wilhelm II of Germany—gained considerable pejorative connotations in English-speaking countries.

German history and antecedents of the title
The Holy Roman Emperors (962–1806) called themselves Kaiser, combining the imperial title with that of Roman King (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.

The rulers of the Austro-Hungarian Empire (1804–1918) were drawn from the Habsburg dynasty, who, after 1438, provided most of Holy Roman Emperors. The Austrian-Hungarian rulers adopted the title Kaiser. There were only three Kaisers of the Austrian Empire, the successor empire to the Holy Roman Empire of the German Nation (Heiliges Römisches Reich Deutscher Nation), and they have all belonged to the Habsburg dynasty. The successor empire to the Austrian Empire was termed the Austro-Hungarian Empire, which had only two Kaisers, both again from the Habsburg dynasty.

In 1871, there was much debate about the exact title for the monarch of those German territories (such as free imperial cities, principalities, duchies, and kingdoms) that agreed to unify under the leadership of Prussia, thereby forming the German Empire. Deutscher Kaiser ("German Emperor") was chosen over alternatives such as Kaiser von Deutschland ("Emperor of Germany"), or Kaiser der Deutschen ("Emperor of the Germans"),[citation needed] as the chosen title simply connoted that the new emperor, hearkening from Prussia, was a German, but did not imply that this new emperor had dominion over all German territories. There were only three Kaisers of the (second) German Empire. All of them belonged to the Hohenzollern dynasty, which, as kings of Prussia, had been de facto leaders of lesser Germany.

In English the (untranslated) word Kaiser is mainly associated with the emperors of the unified German Empire (1871–1918), in particular with Kaiser Wilhelm II. 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.

The Kaisers of the Austrian Empire (1804–1867) and of the Austro-Hungarian Empire (1867–1918) were:
Franz I (1804–1835)
Ferdinand I (1835–1848)
Franz Joseph I (1848–1916)
Karl I (1916–1918)
The Kaisers of the German Empire (1871–1918) were:
Wilhelm I (1871–1888);
Friedrich III (9 March-15 June 1888), who ruled for 99 days;
Wilhelm II (1888–1918), during whose reign the monarchy in Germany ended near the end of World War I.
Georg Friedrich Ferdinand, Prince of Prussia, is currently head of the House of Hohenzollern, which was the former ruling dynasty of the German Empire and the Kingdom of Prussia. Karl von Habsburg is currently the head of the House of Habsburg.

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Frederick III (German: Friedrich III., Deutscher Kaiser und König von Preußen; 18 October 1831 – 15 June 1888) was German Emperor and King of Prussia for 99 days in 1888, the Year of the Three Emperors. Friedrich Wilhelm Nikolaus Karl, known informally as Fritz, was the only son of Emperor Wilhelm I and was raised in his family's tradition of military service. Although celebrated as a young man for his leadership and successes during the Second Schleswig, Austro-Prussian and Franco-Prussian wars, he nevertheless professed a hatred of warfare and was praised by friends and enemies alike for his humane conduct. Following the unification of Germany in 1871 his father, then King of Prussia, became the German Emperor. On Wilhelm's death at the age of 90 on 9 March 1888, the throne passed to Frederick, who had by then been Crown Prince for 27 years. Frederick was suffering from cancer of the larynx when he died on 15 June 1888, aged 56, following unsuccessful medical treatments for his condition.

Frederick married Princess Victoria, eldest daughter of Queen Victoria of the United Kingdom. The couple were well matched; their shared liberal ideology led them to seek greater representation for commoners in the government. Frederick, in spite of his conservative militaristic family background, had developed liberal tendencies as a result of his ties with Britain and his studies at the University of Bonn. As the Crown Prince, he often opposed the conservative Chancellor Otto von Bismarck, particularly in speaking out against Bismarck's policy of uniting Germany through force, and in urging that the power of the Chancellorship be curbed. Liberals in both Germany and Britain hoped that as emperor, Frederick III would move to liberalize the German Empire.

Frederick and Victoria were great admirers of the Prince Consort of the United Kingdom, Victoria's father. They planned to rule as consorts, like Albert and Queen Victoria, and to reform what they saw as flaws in the executive branch that Bismarck had created for himself. The office of Chancellor, responsible to the Emperor, would be replaced with a British-style cabinet, with ministers responsible to the Reichstag. Government policy would be based on the consensus of the cabinet. Frederick "described the Imperial Constitution as ingeniously contrived chaos."

The Crown Prince and Princess shared the outlook of the Progressive Party, and Bismarck was haunted by the fear that should the old Emperor die—and he was now in his seventies—they would call on one of the Progressive leaders to become Chancellor. He sought to guard against such a turn by keeping the Crown Prince from a position of any influence and by using foul means as well as fair to make him unpopular.

However, his illness prevented him from effectively establishing policies and measures to achieve this, and such moves as he was able to make were later abandoned by his son and successor, Wilhelm II.

The timing of Frederick's death and the length of his reign are important topics among historians. The premature demise of Frederick III is considered a potential turning point in German history; and whether or not he would have made the Empire more liberal if he had lived longer is still discussed.

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Wilhelm II or William II (German: Friedrich Wilhelm Viktor Albrecht von Preußen; Frederick William Victor Albert of Prussia; 27 January 1859 – 4 June 1941) was the last German Emperor (Kaiser) and King of Prussia, ruling the German Empire and the Kingdom of Prussia from 15 June 1888 to 9 November 1918. He was the eldest grandson of the British Queen Victoria and related to many monarchs and princes of Europe.

Crowned in 1888, he dismissed the Chancellor, Otto von Bismarck, in 1890 and launched Germany on a bellicose "New Course" in foreign affairs that culminated in his support for Austria-Hungary in the crisis of July 1914 that led in a matter of days to the First World War. Bombastic and impetuous, he sometimes made tactless pronouncements on sensitive topics without consulting his ministers, culminating in a disastrous Daily Telegraph interview that cost him most of his power in 1908. His top generals, Paul von Hindenburg and Erich Ludendorff, dictated policy during the First World War with little regard for the civilian government. An ineffective war leader, he lost the support of the army, abdicated in November 1918, and fled to exile in the Netherlands.