What middle name did J.K. Rowling adopt for her author name?

J.K. Rowling adopted Kathleen as her middle name for her author identity.

Rowling was born Joanne Rowling without a middle name. Before publication of Harry Potter and the Philosopher’s Stone, Bloomsbury asked her to use two initials because it believed boys might be less likely to read a book visibly written by a woman. Rowling chose K in honor of her paternal grandmother, Kathleen.

The result was the professional name J.K. Rowling. The initials do not represent two given names that appeared on her birth certificate. This detail is a frequent source of confusion because many biographies refer to her as Joanne Kathleen Rowling after the name became established.

Rowling later used a different pseudonym, Robert Galbraith, for the Cormoran Strike crime series. That pseudonym is a separate author identity and does not explain the K in J.K. Rowling.