Wesley Rothak is a pony raised by clan Rothak, the guardians of the northern borders of the Griffin Republic. Their clan was entirely devoted to defending the border of the frozen wasteland that dominated the land north of their home, almost entirely populated by colossal abominations of snow, ice, and evil magic.
600 AN (After Nightmare) they sacrificed themselves to destroy the greatest of these abominations and nullify the threat of any that came after.
Which raises the question, how was this pony raised by a bunch of dead griffins?
Due to extenuating circumstances (read: spoilers) little Wesley came into the ability to see, and freely interact with the spirits of the dead.

What he does with this is get himself arrested and serving community service in Ponyville under the direct supervision of the Elements of Harmony, as well as one of Equestria's military elite.