One of two historically substantial chaotic beings, Entropy manifested itself in the form of Pazuzu, a demon prince. Through Pazuzu's influence, the Triumvirate sparked the War of Humanity, allowing Chaos to gain a foothold in Creation.
Entropy joined its brother, Discord, to challenge Proteus in the Chaos Wars. When Ayar, the Creator, realised that His creations were about to be destroyed, He dispersed Entropy and Discord all throughout Creation, adding chaos to it. The Plane of Chaos received the bulk of this dispersal, though chaos everywhere increased.