Orich Alcum the Second's story is an interesting one indeed. Dating back two centuries, to the time of King Aurus, for whom this castle is named, a certain Earth pony blacksmith by the name of Orich Alcum fell in love with a unicorn maiden, whose name has been lost to history. Oddly enough she reciprocated. Since then, and after much fighting on the first Orich Alcum's part, the children of the Alcum family have had dual citizenship within the kingdoms of the Unicorns and Earth ponies. As the king also told me, they also wander between the two kingdoms producing weapons and armor of a quality superior to anything ever crafted prior. Why the king would allow the Alcum smiths to craft weaponry for the Earth ponies is beyond me, but he says it's because that they're just as much Earth pony as they are Unicorn, more so actually. As such they have the right to craft for whomever they please, so long as it isn't the pegasi.
Note: I also learned today that the first Alcum has a rare metal named for him: the appropriately titled Orichalcum.