At first glance, this seems to be an easy question, but from my graduate research standpoint, it is much more difficult to answer than most. Literature Psychology is not a well-known genre. Further, sometimes literature is discussed within academia related to psychology, and sometimes psychology is discussed within academia related to literature. The result is that research on Literature Psychology is not easy exploration. In fact, Literature Psychology is most commonly found under the title of “Psychology and Literature” and focuses on the human behavior found in literary works (especially in regards to character). Further, “the person that created Literature Psychology” in regards to the Psychological Novel is, in itself, a highly debated concept. In short, scholars fight over whether the founder of Literature Psychology (in the form of the Psychological Novel) was Shikibu, Boccaccio, Richardson or Hamsun.
Because Literature Psychology focuses on human behavior, it is important to first understand the focal point where psychologists and literary sages come together. Literature is often used to test theories in psychology (both in regards to characters and in regards to readers). For example, one of the most famous modern examples is the short story “The Yellow Wallpaper” that, for the first time, helped people to understand the psychological issues behind postpartum depression. Scholars of psychology and scholars of literature also come together to help students understand behavior of humanity through the ages. An incredibly recent example of this is the novel The Persian Boy which is actually about the rule of Alexander the Great through the point of view of his eunuch lover, Bagoas. This novel helps many understand the concept of male/male love through the ancient Greek and Persian perspective.
Other scholars who define Literature Psychology admit that there are many literary forms that fit the mold, but believe that the human mind is probed the deepest within the genre of the psychological novel. Because novels are generally long enough to explore characterization most deeply, it is within these psychological novels that we can learn about one or more character’s emotions and feelings and thoughts and consciousness. For example, one can’t help but mention Joyce’s Portrait of an Artist as a Young Man. The title lends itself precisely to the focus on character. The reader is not disappointed. For what follows is a stream-of-consciousness masterpiece that literally lets us probe into the mind of a young artist.
It is in this regard, and in the realm of the psychological novel (also sometimes called psychological realism), that this eNotes Educator can answer your question properly. The irony is that there is more than one answer depending on how one looks at it. You see, what is usually considered the original psychological novel was actually written in the 1200s in Japan by Murasaki Shikibu. It is also sometimes considered “the first modern novel” or even “the world’s first novel.” It is a beautiful account of life at court in the Japan of the middle ages. As one would suspect, the central character is Genji, a prince and son of the emperor. His exploits (such as his family, his stubbornness, his many lovers, his numerous alliances, and his exploration of politics) are the focus of the interior characterization.
However, if you are looking for the first “Western” author of the Psychological Novel as an example of Literature Psychology, we have to mention the author Giovanni Boccaccio from the fourteenth century and his Elegia di Madonna Fiammetta. This is still before the word “psychology” came into existence. Next, if you are only interested in Literature Psychology after the term “psychology” was coined, then we would have to take a look at Samuel Richardson's Pamela. Finally, if you are only interested in the “modern” psychological novel as the first example of Literature Psychology, then we have to go even deeper in to The Encyclopedia of the Novel to find Knut Hamsun’s works such as Hunger.
In conclusion, we could go even further and say that the list of authors above (Shikibu , Boccaccio, Richardson and Hamsun) there is also Literature Psychoanalysis. Noting the grand debate above as to which author should be considered the founder of Literature Psychology, there is less of a debate as to the founder of Literature Psychoanalysis. This, of course, would exist only after the existence of Sigmund Freud and could be the focus of another essay entirely.