The “J” in J.K. Rowling’s pen name represents Joanne, her first name.
Rowling was born Joanne Rowling on 31 July 1965 in Yate, Gloucestershire, England. She later added the initial “K” for Kathleen, her paternal grandmother’s name, when Bloomsbury requested a name that did not obviously identify her as a woman author.
The author has generally been known publicly as J.K. Rowling since Harry Potter and the Philosopher’s Stone was published in 1997. The initials helped create a deliberately ambiguous author identity for the children’s-fiction market.
Rowling has also written crime fiction under the name Robert Galbraith. That pseudonym is separate from the initials J.K., which were used for the Harry Potter books and her novels published under her own name.