The Inspector

One of the most common protagonists in the crime fiction genre, this is a plain clothes police officer who holds the rank of Detective Inspector or Detective Chief Inspector in British works, or Lieutenant in American works. Will often be the older and more senior of a duo, with their subordinate acting as The Watson.

The rank gives you a character with sufficient experience, a good number of subordinates, but at the right place in the chain to be moaned at by Da Chief. Also Inspector sounds right for a detective's rank, even though that's not what it actually means.

Literature

 * DCI Morse.
 * DCI Jack Spratt
 * DI Jack Frost
 * Sherlock Holmes stories had Inspectors Lestrade and Gregson?
 * DCI Thomas Nightingale.
 * Inspector Hemingway, although he's the assistant to Superintendent Hannasyde.

Live Action TV

 * The Bill. 26 seasons on the air, it featured 8 Detective Inspectors among its regular cast during that time. The most famous of them probably being Detective Inspector Frank Burnside.
 * Inspector Kerry Vincent Rush
 * Lieutenant Horatio Caine, CSI: Miami
 * Lieutenant Mac Taylor. CSI New York
 * Lieutenant Fancy in NYPD Blue.
 * An exception with Foyles War- Christopher Foyle is a Detective Chief Superintendent.
 * Detective Inspector Henry Crabbe, Pie in The Sky
 * DI Thomas "Tommy" Lynley, naturally, who forms an Odd Couple crime-fighting duo with his partner DS Barbara Havers.