"This first one's to Gladys Gudgeon, bless her - huge fan of mine - "
-Gilderoy Lockhart (CS7)
When Harry serves detention with Lockhart by helping him answer fan mail, he has Harry address an envelope to Gladys Gudgeon (CS7).
Gudgeon continued writing to Lockhart after his memory was damaged and he became a longterm inpatient at St. Mungo's. Lockhart wasn't exactly sure why she wrote him every week (OP23).
"Gudgeon" = from Latin 'gobion,' variant of 'gobius,' = from Middle English 'gudyon' via Old French 'goujon') something used as bait; a gullible person.