Repairman Jack has no last name, has no SSN, no drivers license, and ignores the laws he chooses to ignore. He fixes situations for people by whatever means necessary. He lives in the intestines of society, just on the other side of the law. . . but he's a good guy who is willing to do what is needed to be done when no one else can help.
The story has a growing supernatural component as the books progress. A couple of movies were made (poorly) from the Repairman Jack universe.
If you like Koontz, you love anything by the writing team of Lincoln Child and Douglas Preston, especially the FBI Agent Pendergast series. Should be read in order as well. These have also had a couple of movies made from them (also poorly) omitting Agent Aloysius Xingu Leng Pendergast, an independently wealthy FBI agent who prefers to drive his antique Rolls Royce while doing investigations.