Ordos is a new world boss located on the Timeless Isle zone, a new island zone added in patch 5.4 to the south-east of the Jade Forest, out in the sea. Where islands usually hang out. According to previous information, Ordos was a boss only accessible by players who had the Legendary cloak. This restriction has now been lifted somewhat, as Blizzard Community Manager Lore notes in the forums:
Just as an update to this:
We're planning to change the restriction for access to Ordos to be account-wide. Basically, as long as at least one of your characters has a legendary cloak, all of them should be able to access the encounter.
This, it seems is a vast improvement, and will make it an awful lot easier for players to find groups to kill Ordos. He's not the hardest boss to take down, but he does have a five-minute soft enrage, so you'll need to be putting out some considerable numbers to get through his health pool, or to have a group that's on the larger side. As a result of this, it seems like a good plan to make it easier to put groups together. What's more, it means you might be able to take out Ordos with your friends.
He seems to be a little bugged on the PTR at present, as I was able to pull him several times with a group, and certainly do not have a legendary cloak on any character! I had fully expected to be kicked off the platform, but wasn't. This will definitely change for live, though!