The following list of German Kings and Emperors is one of several Wikipedia lists of incumbents.
Notes
The relationship between the title of "king" and "emperor" in the area that is today called Germany is just as irritating and complicated as the history and the structure of the Holy Roman Empire itself. The following remarks may or may not clarify things a little (for details, refer to the Holy Roman Empire article):
With the death of the last Carolingian king of East Francia, Louis the Child, the East Frankish nobles elected a replacement. Conrad came from a family as old as the Carolingians, and which had established substantial connections in East Francia.
House of Wittelsbach
Habsburg-Lorraine
In 1806, the Holy Roman Empire collapsed under the military pressure from Napoleon I of France. From 1806 until the foundation of the 1871 German Empire, there was no single leader of a united German territory.
List of emperors of the German Empire