7. Officer Lou
The most competent and genuinely effective police officer in Springfield Police Department (which, true, isn't saying much), Officer Lou is a sergeant who is often seen working closely with Chief Wiggum.
Clancy Wiggum had proven time and time again to be terrible at his job, and when the show decides to remind fans of this fact, Officer Lou is always there to point out his mistakes and question his decisions. Often, he tries to let Wiggum know there's a crime happening right in front of them, but is usually shot down.
One of his best arcs sees him training Santa's Little Helper as a police dog, and though he works best as a running gag to point out the unprofessionalism of his boss, he's also proved to be a solid leading man when given the chance.
Also, without Lou, we shudder to think what the Police Department would look like with his much-needed morals and ethical understanding.