Salazar Slytherin is the overarching antagonist of the Harry Potter franchise. He was one of the four founders of the Hogwards School of Witchcraft and Wizardry and one of the founder of the Slytherin house.
Dumbledore's Army: Ginny Weasley • Luna Lovegood • Fred Weasley • George Weasley • Cho Chang • Dean Thomas • Ernie Macmillan • Hannah Abbott • Justin Finch-Fletchley • Lavender Brown • Seamus Finnigan • Susan Bones • Lee Jordan • Parvati Patil • Padma Patil • Angelina Johnson
Order of the Phoenix: Minerva McGonagall • Arthur Weasley • Molly Weasley • Aberforth Dumbledore • Arabella Figg • Fleur Delacour • Bill Weasley • Kingsley Shacklebolt • James Potter•Prongs • Lily Potter I • Remus Lupin • Sirius Black • Elphias Doge
Voldemort's Followers: Bellatrix Lestrange • Barty Crouch Jr. • Peter Pettigrew•Wormtail
Hogwarts School of Witchcraft and Wizardry: Horace Slughorn • Pomona Sprout • Poppy Pomfrey • Quirinus Quirrell • Filius Flitwick • Helena Ravenclaw • Peeves • Bloody Baron
Ministry of Magic: Cornelius Fudge • Barty Crouch Sr. • Dolores Umbridge • Percy Weasley
Other: Madame Maxime• Fenrir Greyback • Lucius Malfoy • Narcissa Malfoy • Gellert Grindelwald • Dobby • Cedric Diggory • Armondo Dippet • Astoria Malfoy • James S. Potter • Albus Potter • Lily L. Potter • Scorpius Malfoy • Hugo Granger-Weasley • Rose Granger-Weasley • Delphini
Fantastic Beasts: The Crimes of Grindelwald: Nagini • Nicholas Flamel • Vinda Rosier
Fairytale Characters: Altheda • Amata • Antioch Peverell • Asha • • Ignotus Peverell • Ignotus Peverell's son • Sir Luckless • Warlock
Mentioned only: Kendra Dumbledore •Percival Dumbledore • List of Harry Potter characters