H (Harry Potter)
From Fan History Wiki
In 2001, Hermione Granger’s name begins to be shortened to Hr instead of H in order to differentiate her name in referring to pairings like H/D, in which the H stands for Harry. This related to the change in the fandom as it became more slash-centric. H/D no longer worked as it could mean Hermione or Harry. (Cindelius: [1])
