The title for German monarchs, emperors, and other such bigwigs. Don't confuse with Chancellor (as in Bismark), the guy who really runs the show.

Kaisers of note: Wilhelm I - Nice guy, didn't rock the boat too much.
Wilhelm II - I's grandson, an absolute prick, managed to piss off pretty much every government in Europe, and fired the architect of the newly unified Germany, the aforementioned Bismark.

Comes from the Latin Caesar, just like the Russian Czar.