Ellery Queen

• Ellery Queen is a unique fictional investigator in that Ellery Queen is both the name of the detective as well as the pen name for the writers who created him. Ellery Queen is the creation of two men named Daniel Nathan and Manford Lepofsky. Queen has appeared in stories, novels, theatrical films and a TV series.
  
  

Mike Hammer

• The hardest of the hard-boiled private investigators is probably Mike Hammer. Hammer is the creation of Mickey Spillane. While most other investigators work within the limits of the law, Hammer is well known for viewing much of the law as an obstruction to absolute justice. He is willing to break laws and use violence to bring about that justice.
  
  

V.I. Warshawski

• Most fictional private investigators to achieve fame have been men, but the occasional female P.I. has slipped into the consciousness of mystery readers. V.I. Warshawski is a character in a series of novels written by Sara Paretsky. Warshawski tried her hand at bringing about justice as part of the criminal justice system, but left her position as a public defender to go into business as an investigator.
  
  

Kinsey Milhone

• Sue Grafton created another popular female investigator featured in a series of books where the title follows the pattern of "A is for..." Kinsey Milhone also left an official position in the world of law enforcement when she quit her job as a police officer to become a full-time private investigator.
  
  

Hercule Poirot and Miss Marple

• Agatha Christie is a writer who gave the world two memorable private investigators. Hercule Poirot is immediately recognizable by his stiff, waxed mustache. He is Belgian with an affinity for good food and suffers from seasickness. Christie's other great detective is the elderly Miss Marple, a woman that murder seems to follow into the most unlikely of places. While not officially a private detective, Miss Marple is nonetheless a significant literary private investigator who manages to solve crimes that happen routinely around her.
  
  

Sam Spade

• Dashiell Hammett created Sam Spade, another hard-boiled investigator most famous for his case involving the Maltese Falcon. The image seared into the public consciousness of Sam Spade is that of Humphrey Bogart from the movie version of "The Maltese Falcon." The literary Spade is significantly different from Bogey's portrayal in terms of physical appearance. Hammett's Sam Spade is tall and blonde and even more misogynistic.