The Darkmoon Faire Herald or Darkmoon Faire Barker is a member of the Darkmoon Faire that announces the arrival of the Faire. They are only available the week before the Faire is set up, and only to the faction where the Faire will set up.
Kruban Darkblade can be found wandering Orgrimmar the week before the Darkmoon Faire is set up in Mulgore.
Melnan Darkstone can be found wandering Ironforge the week before the Darkmoon Faire is set up in Elwynn Forest.
They start the quest The Darkmoon Faire.
Although the Darkmoon Faire are neutral, the Darkmoon Faire Barker is friendly only to his faction, and will attack players of the opposite faction.