The “J” in J.K. Rowling’s name represents Joanne.
J.K. Rowling was born Joanne Rowling on 31 July 1965 in Yate, Gloucestershire, England. She did not originally have a middle name. Before the publication of Harry Potter and the Philosopher’s Stone, her publisher asked her to use two initials because the marketing team believed that some boys might avoid a book written by a woman.
Rowling chose “K” in honor of her paternal grandmother, Kathleen, and used the combined pen name J.K. Rowling. The name became globally associated with the Harry Potter novels, although “Joanne Rowling” remains her legal and personal name in biographical contexts.
The author later used another public name, Robert Galbraith, for the Cormoran Strike crime novels. That separate name should not be confused with the initials in J.K. Rowling.