The Many Masks of Ernie Macmillan.
He knew everyone thought he was a pompous prat, but he knew better. The pompous act he had flung up in his first year was just one of many masks he had.
Ernie was very adept at putting up highly convincing masks at a moment's notice; he had to be really, what with the ever changing moods of his rather pure-blood minded family. Of course, all pure-bloods were good at putting up masks, but Ernie prided himself at having such a wide variety. He had ones for his best friends, his close friends, acquaintances, enemies, family, teachers, other people of authority (with specific ones reserved for prefects), even a few prepared in case he met any famous people or royalty!
He had hastily put up a mixture of his 'famous people' and 'acquaintances' masks when some people walked into his compartment on the Hogwarts Express in his first year, not knowing who to expect. The result had been a rather pompous, arrogant, eleven year old, and as these people got sorted into Hufflepuff with him, he had to keep up the mask, which became his 'best friends' mask.
Why does Ernie have so many masks? Obviously it's because of his 'pure-blood minded family'. It's a rather large family by pure-blood standards, with six siblings, ranging from twenty to ten years of age. Ernie was the second youngest, with only a sister who was due to start Hogwarts School of Witchcraft and Wizardry the next year. Ernie had so many masks, because it was impossible to be accepted as 'you' in any society, and the pure-blood elite was only harder than other societies in that matter. So Ernie created the masks. At first he made them for his amusement, when he was around six, but then he realised the potential of having a finger in each pie, so to say, and developed them further, giving them backgrounds and personalities.
By the time little Ernie went to Hogwarts, he was well adapted to making and changing his masks at any opportunity. After a few years, Ernie had no idea what his original personality had been like, but he certainly knew how to be cunning and was definitely ambitious – aiming for the political power of the Minister for Magic was ambitious after all.
So it was that the Slytherin minded boy put up a foolish, pompous, Hufflepuff-minded mask, that no-one would approach unless they were Hufflepuffs themselves and recognised another one of their kind, on that fateful first train ride in.
And so it was that, as he surrounded himself with those who would be loyal to him until the very end, that he was more Slytherin than anyone else could hope to be, convincing the Sorting Hat to put him in Hufflepuff where he could plot privately and undisturbed.
And so it was, that after all the fuss about Lord Voldemort had died down, and he was named Minister for Magic, that he had the backing of the whole of Hufflepuff, and much of Ravenclaw and Gryffindor, so no-one really noticed when he subtly changed laws, and had certain people... disposed ... of.
And so it was that little Ernie Macmillan became the most successful Dark Lord in history, and all because of a few masks.