The Beast
The Beast, sometimes referred to as Nightmare or Darkness, was an ancient divine creature that existed under the mountains near Highgate and was a source of all thaumaturgy. It was originally created by Sin to suppress the gods during an era of divine strife, sending them into a deep slumber. However, this had the consequence of releasing corruption throughout the land and waters of Wraeclast, culminating in the devastating Cataclysm of 1339 IC when the thaumaturgist Malachai attempted to control the Beast to gain control of thaumaturgy. Wraeclast was devastated, causing mutations within the living and non-living alike. Many humans were transformed into monsters and the dead were reanimated across the cursed land.
An exile was responsible for killing the Beast around 20 years prior to the events of Path of Exile 2, causing the slumbering gods to awaken throughout Wraeclast. Many of these gods were also slain, but several others still remained. Traces of corruption still remain, and Count Geonor was among those who wanted to harness the lingering powers of the Beast for his unknown purposes. Within the forests of Ezomyr he discovers a Seed of Corruption, setting the stage for the events of Path of Exile 2.