Hamish Piper

Personality
Laid back, snarky, a bit of a player, or at least he fancies himself one, Hamish doesn't have to work for much in his life thanks to his musical powers, and it shows, he often comes off as lazy and opportunistic, if not a bit of a snake oil salesman, although when needed he can be charming he doesn't really care to much.

Hamish does have a bit of a temper, and tends to react when he feels he's been crossed in some way, he or his family. Very much prone to an eye for an eye, this retalition however usually takes the form of public humiliation or mischief as opposed to outright violence.

His parent's don't really know how to dicipline him on this little problem, seeing as it's very much in keeping with his eventual plot. But at the same time, it's kind of an issue.

Appearance
Tall and lanky Hamish is quite handsome, although there is some undefinable rat-like quality about his eyes and nose. His hair is odd, being a sandy sort of grey on top and black beneath. It's possible he dyes it, but he swears up and down it's natural just like his sharp orange eyes. He usually slouched or leans against something, as if it were just too much trouble to fully support his own weight and when he smiles or smirks, which is often it's been commented he looks charmingly rakish.

The Story
The Wikipedia has a pretty detailed description of both the story itself and the history of the tale.

The story of The Pied Piper is a simple one, the town of Hamelin is plagued by rats, so many rats the people are swimming in them. Then The Piper comes along. He offers to rid the town of rats for a price. And the mayor agrees. So the Piper does it, and all but one rat drowns. The Piper returns feeling quite proud of himself, and demands his money, at which point the mayor laughs at him. Because no, they aren't actually going to pay him. (In some versions they offer him much less money, in some it's because they offered to pay by head, and he didn't bring any heads.)  So the Piper leaves, swearing vengeance. VENGEANCE I TELL YOU!

The Piper does indeed return. Dressed in green like a hunter. And he lures the children of the town away, what he does with them varies on the retelling, from drowning them in the river to abandonening them in Transylvania. Or even returning them after being paid the gold he's due.

How does Hamish come into it?
Some time after leaving the children in Romania The Pied Piper continued his journey stopping at an inn he met a most entrancing dancer. The two of them hit it off immediately and set out together, carrying on with the travelling rat removal/ con person/ shister business, until Mrs. Piper noticed she was getting a little chubby, realizing that they couldn't keep up the game with a kid in tow they settled down in the village of Book End, The Piper getting a job at Ever After High. Some months later, Melody was born.

Hamish himself came along a couple years later, just to round out the American dream family, two parents, two kids, and a house full of brainwased rats. His destiny was apparent from very early on. As he like the rest of the family picked up music with alarming speed, but little critters tended to fall in line after him whenever he played. And pretty soon he realized he could use that talent on bigger animals.