TV detectives were once paragons of manly competence. Mannix, Peter Gunn, Kojak, all of these were masterful males.
Then came an interregnum. In the 1970s and 80s, we saw a new crime solver: Magnum PI, Jim Rockford of the Rockford files, and Columbo. All these characters practiced self deprecation. They actually made jokes against themselves. Plots sometimes unfolded at their expense. Occasionally, they were made to look foolish.
And now the present crew: Jethro Gibbs (Mark Harmon on NCIS), Horatio Caine (David Caruso on CSI: Miami), Mac Taylor (Gary Sinise on CSI: NY) and Gil Grissom (William Petersen of CSI: Crime Scene Investigation) all of these characters appear to take us back to the old model.
Grissom can be a little quirky and bookish. Occasionally, Gibbs exhibits a sense of humor. But Caine and Taylor are dour and melodramatic. The idea of self deprecation! Never! Occasionally, these characters endure inner conflict, but this never rises to the level of real complexity and never ever are they allowed to get down off the high horse of steely competence and manly self control.
Now, we know that the while these shows were taking shape, there were two crime dramas on cable, Homicide and The Wire, that were doing what cable is done so well elsewhere, opening things up for the mainstream players. More recently, Monk and Psych have offered almost perfect inversions of the usual model. So there was both precedent and inspiration for a more complicated view of the lead detective.
Furthermore, we know this character descends in part from Sherlock Holmes who was flawed and conflicted. He also descends from the Noir detective that Humphrey Bogart captured so well and the Noire detective was nothing if not complicated clock work.
But most important, there was a brief moment in popular culture in which the detective took on a sense of humor.