Edgar Derby is one of Billy Pilgrim's fellow prisoners of war. He seems a decent person and one of the few who understand the effects of war on a man although he is older and had to pull strings in order to even join the army.
Howard W. Campbell is an American who lived in Germany before the war and spread propaganda for the Nazis. In fact he writes a long treatise about the inferiority of Americans to Germans. He tries to recruit some of the prisoners by referencing their own dirty and sad state. Derby is the only one who stands up to him and calls him out on his traitorous ways.
After the fire bombing of Dresden, Edgar Derby is executed for stealing a teapot. Vonnegut is pointing out the absurdity of war and human behavior. Thousands of innocent people have been incinerated by American bombs, but Derby is killed for a petty theft.