How about ‘Krummbein’ from Harry Potter as suggested by
http://www.katzenfreund.com/katzennamen_kater.htm
Not all of them are of German origin though.
And please no names from the Third Reich. When you have visitors from Germany (maybe at some point in the future, you never know) and you introduce your cat as Himmler or Der Führer, the visitors will be very offended. I’m not kidding. Panzerfaust might be viewed as being mildly funny, especially when your cat is very aggressive, but again it gives the impression that your association with Germany is mainly about Nazism and the second world war. Your German visitors would silently pity you as an ignorant American while trying to remain polite.
Suppose Barack Obama visits Germany and Angela Merkel introduces her cat to him, a tomcat she named Jim Crow. Now what would Mr. President think of that?