Who is Uncle Karl from Daniel Half Human and what is their importance?

Uncle Karl is Rheinhard Kraushaar's law partner. Rheinhard takes Karl in as a young lawyer and teaches him the profession. When the Nazis pressure Karl to force Rheinhard out of the practice because his wife is Jewish, Karl tries to convince Rheinhard to divorce her. He also offers Rheinhard a job at his brother's furniture factory, but Rheinhard refuses. Over time, Karl throws Rheinhard out of the practice.