WoWDB

"This boss requires you to have the Patch 5.4 legendary cloak to access him."

For those needing to catch up, you can read an overview of Wrathion's legendary quest chain here.

Edit:  With Warlords of Draenor, you no longer need the legendary cloak since the quest chain was removed from the game.

(Easier to reply to myself than try get WoWDB to let me edit my old comment.)

You actually still need to have acquired the MoP legendary cloak on at least one character.  Blizzard jumped the gun on that patch change, and they've not revisited it since.  I don't think we can expect to ever have them fix the problem that kept the anticipated patch change from working.

Ordos drops Normal—Warforged quality gear.  You can use a Bonus Roll for his loot, but you are limited to once per week for a chance at gear from killing Ordos and from using a roll.

Raid Information does not track 'lock-outs' to any of the world bosses. Since at this point none of the pre-5.4 world bosses are relevant, use the following macro (doesn't matter if your character is Alliance or Horde) to double-check if:

• Any Celestial has been killed
• If Ordos has been killed
• If you remembered or not to complete the weekly quest for  Warforged Seal

/run for k, v in pairs({Celestials = 33117, Ordos = 33118, WarforgedSeals = 33134}) do print(format("%s: %s", k, IsQuestFlaggedCompleted(v) and "\124cff00ff00Done\124r" or "\124cffff0000Not Done\124r")) end

Credit to lostoutcast.