The 35 characters who appeared in all 7 books are:

Harry
Hermione
Ron
Ginny
Neville
Fred
George
Dumbledore
McGonagall
Hagrid
Molly
Hegwig
Fang
Nearly Headless Nick
Seamus
Dean
Snape
Malfoy
Crabbe
Goyle
Percy
Peter Pettigrew
Vernon
Petunia
Dudley
Katie Bell
Parvati
Flitwick
Madame Pomfrey
Professor Sprout
Lavender
Peeves
Filch
Mrs Norris
Fat Lady