No one has sold more mysteries than Agatha Christie. She created two popular sleuths. The first was Hercule Poirot, a tretired Belgium police detective turned private eye. The second is Miss Jane Marple, a spinster sleuth extraordinaire. Everything in an Agatha Christie book is related to the question of who did it. Christie's stories have delighted readers for decades.
Robert B. Parker
Parker's most famous character is Spenser, the private investigator from Boston. Spenser was introduced to the world in 1972. A modern version of the private eye, he is a tough guy with a code of honor. Spenser also works with a team of people. Robert B. Parker also wrote books about other characters, including private eye Sunny Randall and police chief Jesse Stone.
You may recognise Sue Grafton as the author of the alphabet books. Grafton created Kinsey Millhone, a smart, tough private investigator in 1982 A is for Alibi. Kinsey is a former cop turned private eye. Readers love the small details that Grafton writes about Kinsey which make readers feel that they personally know the P.I.
Hillerman created the two characters Sergeant Jim Chee and Lieutenant Joe Leaphorn. Chee and Leaphorn live in the Southwest part of the United States, which is different from other mysteries that take place in large cities. Hillerman introduced mystery readers to Najavo culture and customs and proved that setting is important to solving a mystery.
No mystery author has consistently pleased readers with a police procedural series. Connelly created Hieronymous "Harry" Bosch who is a police detective in Los Angeles. Connelly's books are character-driven with a vivid sense of gritty realism. Bosch is a complicated, conflicted protagonist that struggles with the day-to-day struggles that all police officers endure.