J.K. Rowling’s middle initial in her commonly used name is K.
Rowling was born Joanne Rowling, without a middle name. For publication, Bloomsbury asked her to use two initials because the publisher believed that a gender-neutral name might appeal more broadly to young readers. She chose K to honor her paternal grandmother, Kathleen Ada Bulgen.
Her first Harry Potter book was therefore credited to J. K. Rowling rather than Joanne Rowling. The initials became one of the most recognizable author names in modern children’s literature.
The name is often misread as representing two given names that Rowling used from birth. That is not the case: the K was adopted for her author identity. Rowling has also published crime novels under the pseudonym Robert Galbraith, a separate name chosen for her adult fiction.