Ernie Macmillan is a fictional character from the Harry Potter Universe.
Ernie Macmillan as played by Louis Doyle.
Ernie, according to himself, was completely pure-blood, and was also distantly related to Sirius Black. Unlike other wizards who were proud of their blood status, Ernie would not choose his friends based on blood, as seen with his muggle-born friend Justin Finch-Fletchley. Ernie was also a talented boy who did well in school.
When Ernie arrived at Hogwarts, he was sorted into the Hufflepuff house and befriended fellow Hufflepuffs Justin Finch-Fletchley, Susan Bones and Hannah Abbott. He was rarely seen without at least one of his friends.
During his second year at Hogwarts, Ernie was among those who believed Harry Potter was the Heir of Slytherin. Ernie told Hannah Abbott his theories, and all of his friends believed him. His thoughts of Harry became even worse when Justin was petrified, and Ernie gave Harry the blame when Harry was found at the scene.
However, when Hermione Granger, Harry's own friend, was petrified, Ernie knew he had been wrong, and deeply apologied to Harry for suspecting him. Justin was later unpetrified and could also tell that the Basilisk was what had attacked him, even though it had already been killed by Harry.
During his fourth year at Hogwarts, during the Triwizard Tournament, Ernie was supporting Cedric Diggory as he put his name in the Goblet of Fire. Cedric was chosen, however, Harry Potter's name was also spit out of the flames, once again giving Ernie bad thoughts about him. He was among the students who promoted the pro-Diggory badges, wearing one all the time and showing it to Harry whenever he passed. However, at the end of the tournament, Cedric Diggory was killed by Lord Voldemort himself, Ernie was shocked at the death of Hufflepuff's pride and decided to believe Harry when he told the crowd of Cedric's tragic death.
In his fifth year, Ernie was elected to represent Hufflepuff as a Prefect together with Hannah Abbott. He was one of Harry's biggest supporters and joined Dumbledore's Army right away, which both showed his support of Harry and despise of Dolores Umbridge, who was the reason why the rebel organisation was founded. However, he was worried about his O.W.L.s, studying almost ten hours every day.
The following year, Ernie had Potions classes together with Harry, being the only Hufflepuff who was able to continue with Potions. He shared table with Harry, Ron and Hermione, but was not aware of the fact that Harry was given instructions through the Half-Blood Prince's book.
When the Death Eaters attacked the school near the end year, he presumably did not receive the signal from Dumbledore's Army which would have called him to battle, likely being asleep at the time. However, he was waken up by the noisy battle, and stumbled into Harry who was running after Snape and Draco. Ernie asked what was going on, but Harry kept running and didn't respond. After learning of Dumbledore's death, Ernie paid respect by visiting his funeral.
Because of his blood status, Ernie was allowed to return to Hogwarts, which was now under the control of Death Eaters, with Severus Snape as headmaster. Justin was, however, not allowed to return, so Ernie and Hannah was quite much alone that year. They joined the newly revived Dumbledore's Army, being led by Neville, Luna and Ginny. In rebellion, they did anything they could to bug the new teachers, the Carrows, even though they knew they would be brutally punished. He fought during the Battle of Hogwarts, proving his magical skill by summoning a perfect Patronus, resembling a boar.
- In the comic relief book Quidditch Through the Ages, Ernie Macmillan was listed as having borrowed the book from the Hogwarts library.