Unicorn of Ponyville

From Equestripedia, the Archives of Equestria!
Twilight Twinkle, the only known Unicorn of Ponyville

"Unicorn of Ponyville" was a special title given to a unicorn, presumably from a big city like Canterlot or Canterbury, who moved to Ponyville, presumably to use their magic to help out the primarily Earth Pony demographics. Presumably, other towns were to have a similar Unicorn fill in the role. The only known Unicorn of Ponyville was Twilight Twinkle.