The hardboiled private detective appears in the very first film noir movie, as Humphrey Bogart's Sam Spade in “The Maltese Falcon.” Sam Spade was one of the most popular of the pulp magazine private eyes, and he still exemplifies the archetype.

Sam Spade is a wisecracking, two-fisted, whiskey-drinking tough guy with a stream of cynical commentary and a secret strain of nobility. Bogart played the other really famous PI the exact same way when he took on the role of Philip Marlowe in “The Big Sleep.”

The hardboiled private eye is Raymond Chandler's “shopworn Galahad,” a man who can walk down the meanest streets without himself being mean. He's the most familiar of the noir archetypes other than the femme fatale, but there are those who feel that this type of character can never truly be noir.

The PI is the moral touchstone in noir's amoral landscape of corrupt politicians, sinister old rich men and gunslinging gangsters. He's the one and only incorruptible character, even if the armor of this particular knight is not always shiny. Because the noir detective is a sympathetic character, the very blackest of film noirs often do away with him completely, building the story around a two-bit grifter or a gangster or some other morally compromised character. There's something sentimental about the hardboiled private eye, so that he is never really of the noir universe even though he is often found in it.

More recent incarnations of the hardboiled PI, like Burke or Easy Rawlins, are usually a lot less incorruptible. However, they still retain the same secret nobility under the facade of criminality.