The Tariel are a secret society that has been around for ages, probably around the time the Grand Assembly was founded or a bit after or before it. Fact is, they have been around since the Age of Foundation and carefully watched Horhsal's history. Sure, they don't have influence everywhere and less so in present times compared to earlier ages but they are still around and carefully conducting their plans. What exactly these plans are is hard to tell, especially the question what their ultimate goal is.
Tariel might be responsible for a few cases where information in history was lost, forcibly removing it so it will not be remembered or does not fall into the wrong hands, like what the strange powers of the Ladunrians were and even a few reports of the last Atypian Emperor before the Colossal Chasm was created. It is hard to tell why they removed such pieces of information from history, be it for their own gain or because the information might be dangerous.
Their "work" became a whole lot harder in the Age of Expansion because of the rise of archaeologists and historians, quick information exchange through the Internet, and stronger governments. As such, they have been less active when it comes to their usual doings and focused more on other matters, like building up an information network, earning money, getting more members, and the like.
The Tariel are still a mystery and nobody can be sure whether their intentions are benevolent or vile.
Edited by Gota