Key: Last Name, First Name - Book first appears in. Short summary.
Macmillan, Ernie - Book 2. Hufflepuff boy who often jumps to conclusions.
Macnair - Book 3. Disposes of dangerous creatures for the Ministry of Magic, also a Death Eater.
Malfoy, Draco - Book 1. Harry's archrival at Hogwarts. A Slytherin who struts about, talking about his pure-blood family and insulting everybody else.
Malfoy, Lucius - Book 2. Draco's father. Used to be a school governor and Death Eater. Holds a grudge against Mr. Weasley.
Malfoy, Narcissa - Book 4. Draco's mother.
Malkin, Madam - Book 1. The owner of "Madam Malkin's Robes for All Occasions" in Diagon Alley.
Mason, Mr. and Mrs. - Book 2. Mr. Dursley's business partners.
Maxime, Madame Olympe - Book 4. Headmistress of Beauxbatons Academy, and a half-giant.
McGonagall, Prof. Minerva - Book 1. Deputy Headmistress, Head of Gryffindor House, and Transfiguration teacher at Hogwarts.
Midgen, Eloise - Book 4. Student who tried to curse her acne off, and removed her nose instead.
Moaning Myrtle - Book 2. A sulky ghost who haunts a girls' toilet.
Montague - Book 3. Chaser for the Slytherin Quidditch team.
Moody, Professor Alastor "Mad-Eye" - Book 4. Defense Against the Dark Arts teacher in Harry's fourth year. In his prime, he was an Auror, finding people working for Voldemort.
Moony - Book 3. Professor Lupin's nickname in school.
Moran - Book 4. Chaser for the Irish Quidditch team.
Mostafa, Hassan - Book 4. The Chairwizard of the International Association of Quidditch, and referee for the Quidditch World Cup.
Mulciber - Book 4. Sent to Azkaban for supporting Lord Voldemort.
Mullet - Book 4. Chaser for the Irish Quidditch team.