The middle initial in J.K. Rowling’s professional name is K.
Rowling was born Joanne Rowling and did not have a middle name. Before the first Harry Potter novel was published, her publisher asked her to use two initials because it was thought that some boys might be less likely to read a book written by a woman. Rowling selected K in honor of her maternal grandmother, Kathleen.
The name became J.K. Rowling, with J standing for Joanne. In later interviews and biographies, the author has clarified that the K is an adopted initial rather than an abbreviation of a middle name recorded at birth.
Rowling has also published under other names. Her crime novels use Robert Galbraith, while her 2020 children’s novel The Ickabog was released under her own name. These different bylines reflect publishing choices and genre identities, but J.K. Rowling remains the name most closely associated with Harry Potter.