J.K. Rowling’s first name is Joanne, her full name being Joanne Rowling.
Rowling was born Joanne Rowling on 31 July 1965 in Yate, Gloucestershire, England. The initial “K” was added when her publisher requested a second initial for the Harry Potter books; Rowling did not have a middle name, so she chose Kathleen in honor of her paternal grandmother.
The name “J.K. Rowling” became her public author identity, although the initials can obscure her given name. She has also published crime fiction under the pen name Robert Galbraith. “Jo” is a familiar form of Joanne, but it is not the full first name asked for here. Her published memoirs and biographies generally identify her as Joanne Rowling, later Joanne Murray during her first marriage.