Exodus

Exodus is the main villain of Ultima III. It was created by Mondain and Minax, who considered Exodus their "child".

Exodus is part Daemon, part magical entity and part machine. The Daemon part is Exodus' psyche, his personality and lifeforce, while the machine part is Exodus' power and knowledge, most of it contained in a device similar to a hard drive, called the Dark Core. The "magical" part is probably what allows Exodus' Deamon and machine parts to work together.

Exodus waited a long time after the death of his creators, gathering information about the world and about his enemies. Exodus appears to have a great curiosity, wanting to learn about everything. Most of the information he collected was trivial, like the color of the sky at one specific day; while he also was able to learn about how to manipulate the very being of the world itself.

In Ultima III Exodus attacked, poisoning the spirit of the land itself while his hordes roamed Sosaria. He raised the Isle of Fire from the bottom of the sea and turned it into his fortress, building the Castle of Fire. He protected the Isle with the Great Earth Serpent, which he had ripped out of the void and enslaved to his will. The abduction of the Serpent in turn caused the War of Imbalance on the Serpent Isle.

Exodus' end came when the Stranger together with their companions successfully invaded the Castle of Fire. They used the Four Cards to destroy or deactivate the machine part of Exodus, though the Dark Core itself survived. The destruction of the machine caused the daemon Exodus to vanish from the world.

But even this wasn't the end of Exodus. His psyche was somehow captured shortly after his death by the Gargoyles, who fused it into the Shrine of Diligence. The capture of Exodus' psyche destabilized the Isle of Fire, which sank under the sea. The Avatar met Exodus in the Shrine of Diligence in Ultima VI. By that time Exodus regretted what he had done, having had enough time to think about it.

His leftover machine part, the Dark Core, reappeared in Ultima VII after the Isle of Fire surfaced once again from the seas. The Avatar managed to throw the Dark Core into the void, preventing it from reattaching Exodus' psyche to it, which could have resurrected Exodus.

Trivia

 * The Four Cards needed to destroy Exodus are computer punch cards, showing Exodus' technological origins.