Which pseudonym did J.K. Rowling use for the Harry Potter companion book Quidditch Through the Ages?

J.K. Rowling used the fictional author name Kennilworthy Whisp for Quidditch Through the Ages.

Quidditch Through the Ages was published in 2001 as a companion volume to the Harry Potter books. It is presented as a history of the wizarding sport, covering its development, rules, equipment, teams, and famous matches. In the fictional book, Kennilworthy Whisp is credited as the author.

The companion book was issued alongside Fantastic Beasts and Where to Find Them, with proceeds benefiting Comic Relief. Readers sometimes confuse Whisp with Newt Scamander, who is credited with Fantastic Beasts, or Bathilda Bagshot, the fictional historian associated with A History of Magic. These names belong to different books within Rowling’s invented bibliography.