Edgar Allan Poe has been hugely influential in the literary world since he began publishing in the mid-1800s. His texts have served as exemplars of how to use sensory detail and how to establish and evoke mood through description. He also set the standards for Gothic and detective fiction with his famous short stories.
Poe is famous for his ability to create a mood in his literary works, often a sinister and/or foreboding mood. Many of his stories establish suspense and mystery through the mood that he evokes. "The Fall of the House of Usher," for example, opens with a lengthy description of the house and the lake outside the house, which reflects the house in its water. The details given in the first several paragraphs establish the themes of decay and death and set an ominous tone for the story.
Poe's inventive use of language also led him to coin some of his own words. Poe is credited with creating the detective story and as being the best-known contributor to the Gothic tradition in American literature. One could argue that even today's horror movies are influenced by the precedent set by Poe.
In his short stories and poetry, Poe is also known for his interest in psychology. He often portrays unstable and/or unreliable narrators who sometimes descend into madness over the course of the story. As much Gothic literature does, Poe is interested in the way that extreme conditions or traumas might affect a character's psychology and actions. About fifty years later, the Modernist movement in literature would become even further interested in psychology and even try to replicate the way the human mind operates through stream-of-consciousness narrative style.
Poe also served as an influence on famous and accomplished international writers like Jorge Luis Borges, a South American writer known for his magical realism. As a short story writer, Poe established the theory that a good short story should be able to be read in one sitting and that its effect can only be truly felt if all of the details of the story contribute specifically to the plot and theme. Many short story writers have obviously followed his lead, as he was a forerunner in the genre.
In sum, not only did Poe produce some of the most famous and admired works of American literature that we still teach and read today, he also influenced writers in multiple genres and showed us what it is possible to accomplish in a work of literature.