Dashiell Hammett - In his early life, Hammett was a prolific writer with more than 80 short stories, many of them serialized in the Black Mask, and five novels. Hammett is noted for his realism, his crisp, colorful language, and his “lean” story-telling style. He was a major influence on Raymond Chandler, who said of Hammett in The Simple Art of Murder: “He was spare, frugal, hard-boiled, but he did over and over again what only the best writers can ever do at all. He wrote scenes that seemed never to have been written before."
Raymond Chandler - Chandler began his writing career at the age of 44 by publishing short stories in the Black Mask. Dashiell Hammett's Sam Spade and Chandler's Philip Marlowe are considered to be the original hard-boiled detectives. They paved the way for Ross Macdonald's Lew Archer, John D. MacDonald's Travis McGee, Robert B. Parker's Spenser, and Michael Connelly's Harry Bosch, among others. Chandler's ability to depict the California setting so that it became a metaphor for both the opulence and decay of modern American society also had a major influence on the works of both Ross Macdonald and Michael Connolly.
Erle Stanley Gardner - Gardner began his writing career by contributing short stories to the pulp magazines of the day. He was a regular and popular contributor to the Black Mask under the pen name Charles M. Green. Renowned for his Perry Mason novels, he described the character as “a fighter possessed of infinite patience”. Gardner drew upon his own experience in creating Mason: his love for trial work and his defence of the underdog. His creation of a lawyer/crime solver in the character of Perry Mason laid the foundation for such modern-day characters as John Lescroart's Dismas Hardy and Michael Connelly's Mickey Haller.
I've adapted some of this material from my Open Investigations blog, where you can find my original posts on Hammett, Chandler, and Gardner.