The following image is a family tree of every king, monarch, confederation president and emperor of Germany, from Charlemagne in 800 over Louis the German in 843 through to William II in 1918. It shows how every single ruler of Germany was related to every other by marriages, and hence they can all be put into a single tree.
'King of Germany' does not necessarily mean that the king was referred to as such, although in every case he was both de jure and de facto ruler over the territory currently known as Germany and hence the various terms are practically equivalent. Until 911 the kings were known as 'Kings of East Francia'. After that the title fluctuated between 'King of Germany' and 'King of the Germans'. From Henry IV on the kings were "German King (technically King of the Romans)", a reference to the claim on Rome, although this was not often actually ruled by them.