J.K. Rowling’s Harry Potter books were published under the initials J.K.
Rowling was born Joanne Rowling and did not have a middle name. Bloomsbury, her British publisher, asked her to use two initials on the cover of Harry Potter and the Philosopher’s Stone. The publisher believed that a gender-neutral presentation might appeal more broadly to young readers, particularly boys.
The “J” stands for Joanne. Rowling chose “K” in honor of her paternal grandmother, Kathleen, although Kathleen was not part of her birth name. The initials became her public author identity and were retained across the Harry Potter series and many later publications.
In the United States, the first book was published as Harry Potter and the Sorcerer’s Stone, but the author’s initials remained J.K. Rowling. Rowling later used her full name for some projects and the pseudonym Robert Galbraith for the Cormoran Strike novels, so the publishing name depends on the work.