J.K. Rowling’s first name at birth was Joanne; the initial “K” was added for publishing.
Rowling was born Joanne Rowling in Yate, Gloucestershire, in 1965. She has no middle name beginning with K. For the publication of Harry Potter and the Philosopher’s Stone, her publisher requested two initials because it was thought that a gender-neutral author name might appeal to boys as well as girls. Rowling chose K in honor of her paternal grandmother, Kathleen.
The author therefore became known publicly as J.K. Rowling even though her birth name did not contain a K. She has also published under the name Robert Galbraith for the Cormoran Strike novels. The initials are part of her professional name, not evidence that she was born with two given initials.