Hartigan has spent time in jail for rapes he did not commit. He knows that Roark Junior is responsible and has been committing the same crimes since his incarceration. Now that he has been released he is determined to put a stop to him. His motives become stronger once he learns that Roark Junior now has captured Nancy, his long time pen pal and daughter like friend. Hartigan refused to let one more girl be hurt by this Yellow Bastard and will do anything in his powers to stop him.
Good vs. Evil:
Hartigan is a soon to be retired cop. For the entirety of his career he has worked to uphold the law and keep citizens of Basin City safe. He is now faced with the challenge of standing up to the Roark family. With generations of corrupt landowners and politicians, their family has a large influence over the city and tend to get away with whatever they please.
Morality
The Yellow Bastard is violating many aspects of a human's moral code. He is raping and killing young girls all for his own satisfaction. He commits these crimes and knows he can get away with it because of how powerful his family is. By taking the lives of innocent girls he is directly interfering with their abilities to live a happy life. Hartigan feels that it is his duty to stop him to restore moral order in the city and to clear his own name. In order to save Nancy's life, he believes that he must kill himself. The idea of suicide is not right in human morale, but he chooses to take his own life to save another.
Symbols
Title:
The title "That Yellow Bastard" stands for much more than meets the eye. Calling someone a "yellow bastard" is slang for calling them a coward or a cowardly person. Roark Junior is a coward for hiding behind his family and using Haritgan as a scapegoat.
Yellow:
There is now clear reason why the yellow bastard (Roark Junior) is yellow in the books, but there are many theories. Many believe it is connected to the "yellow bastard" saying and that by coloring him yellow helps to verify his name and play on the meaning. Others believe that it may have to do with the "complications" of having his parts reconnected after Hartigan shot them off. It is also believed that the color yellow may symbolize evil which could be another explanation for Miller's choice in colorization.