The brother of Wilhelm Rüstow and Alexander Rüstow, Cäsar Rüstow was one of the foremost experts of his time in the design and construction of military rifles, and the writer of several treatises on that subject, notably "Die Kriegshandfeuerwaffen" (Berlin, 1857–64). Both Alexander and Cäsar fell on the field of battle in the war of 1866, Cäsar at the Battle of Dermbach. He was the grandfather of the sociologist Alexander Rüstow.