The Ire are Worldhoppers from Sel, their upper echelons are composed of Elantrians. In Mistborn: Secret History, their skin tone is mentioned as being silvery, they speak of Devotion, one of the Shards on Sel, whose Vessel's name was Aona, from which comes the word Aon. Their name, 'Ire', is the Aon for age. They seem to be capable of a lot, Khriss said they'd had been at it a lot longer than she had. They knew how to overcome the biggest problem with Selish magics: that they get weaker the further one goes from the region they call home, They seem to be using giant pipes to draw energy from the Dor. They knew how to traverse the Cognitive Realm safely, they knew things about the Shards, how to manipulate Connection, etc.
We know that were pre-Reod Elantrians, that is they were from before the earthquake that created the chasm which caused the city to fall, the Shaod and Aons to malfunction, and affected the Seons, especially those who were bonded to Elantrians. Yet the Ire didn't intervene, so they might not have been affected by it.
I have a theory that the Ire were the original builders of the city of Elantris.