President of Germany
Friedrich Ebert (SPD) served as Germany's first president, followed by Paul von Hindenburg. The office effectively came to an end upon Hindenburg's death in 1934 and its powers merged with those of chancellor. Adolf Hitler now ruled Germany as "Führer und Reichskanzler", combining his previous positions in party and government. The office, however, was not abolished and briefly revived at the end of the Second World War when Hitler appointed Grand Admiral Karl Dönitz as his successor as President of Germany. Dönitz agreed to the surrender to the Allies and was arrested a few days later.
Kaiser
With the Unification of Germany (aside from Austria) in 1871, there was some 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 new German Empire. The first Kaiser himself preferred either "Kaiser von Deutschland" ("Emperor of Germany") or "Kaiser der Deutschen" ("Emperor of the Germans"). In the end, his chancellor Bismarck's choice "Deutscher Kaiser" ("German Emperor") was adopted as it 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, especially since the "Austrian Kaiser" would have been offended as Austria, inhabited by Germans, was still considered part of the German lands. 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 (Germany excluding Austria).