The League of Extraordinarily Gifted People
The Tarrasque is an enormous creature, which normally sleeps deep within the mantle of the world. However, it was determined by the Mages of Al Hanir that roughly every 3,400 years, the Tarrasque would stir and rise to the surface in order to wreak havoc upon the world. The mages were also able to determine that the Tarrasque seemed to always emerge in the same location, namely, within The Nentir. The Mages of Al Hanir decided to magically isolate the Nentir, in hopes of limiting the rampage of the Tarrasque. That spell, which involved regular sacrifices of sentient beings, was interrupted and ended by The League of Extraordinarily Gifted People, after they had been captured in order to be sacrificed.
The Tarrasque emerged in the Nentir, as predicted and has caused much death and destruction in that realm as well as in Old Nerath. The last you’ve heard, the Tarrasque is in the north of Old Nerath.
The Tarrasque’s origins are not clear, although its destructive and wild nature makes it a likely creation of the Primordials. Also unclear, is how the Tarrasque’s previous rampages have ended. For example it is unknown if the Tarrasqe merely retires itself back into the earth or if it must retreat from battle or otherwise be subject to a spell.