Ernest "Ernie" Macmillan (b. 1980) was a pure-blood wizard who attended Hogwarts School of Witchcraft and Wizardry from 1991-1998. He was in the same year as the famous Harry Potter and was sorted into Hufflepuff House. He was also born into the Macmillan family, one of the Sacred Twenty-Eight.
Ernie was an academically strong student and good friends with Hannah Abbott and Justin Finch-Fletchley. In 1992, Ernie initially suspected that Harry Potter was the Heir of Slytherin during the opening of the Chamber of Secrets in his Second year. However after Hermione Granger was petrified he told Harry that he knew Harry would never do that to her. After he apologized to Harry for his suspicions and accusations, the two became good friends