Evil Deities

Evil Deities or Demon Gods were legendary figures in the New World, who appeared some time after the demise of the Eight Greed Kings. Evil Deities spread chaos and destruction throughout the land until they were all eventually defeated by the Thirteen Heroes.

Background
Not much is known about what the Evil Deities were, or their number. They were estimated to be immensely powerful by New World's standard. Evil Deities only desire, as far as anyone knew, was to destroy everything in their path. It is also believed that they were not beings originally from the New World, much like their predecessors, the Six Great Gods and the Eight Greed Kings.

According to the dwarves' history of the Dwarf Kingdom, its country's capital Feo Berkana was once targeted by one of the Evil Deities who is the cause for killing most members of the royal family. In addition to that, many countries had been destroyed by the Evil Deities two hundred years ago, which was why there are very few countries with no more than two hundred years of history.

It was not just human kingdoms that were destroyed during that era. Countries populated by demi-humans and other heteromorphic species perished as well. Within their ranks was the Demon God of Insects, which the Platinum Dragon Lord and Evileye spoke of when battling alongside the Thirteen Heroes. However, it is unclear if this being was either one and the same kind they were fighting together or possibly more than one of them fought separately.

Moreover, a being known as the king of the demons, the Demon God had led demons under his banner while having almost exterminated the entire world. The Demon God had met its end at the hands of the Thirteen Heroes, which vanquished it, and in a certain place, it was still possible to see traces of that battle.

Also, there was once a being called the 'God Dragon' who became the last and final opponent for the Thirteen Heroes to have fought against during their adventures together.

In the Web Novel, their battle with the God Dragon marked the end of the Thirteen Heroes as they were said to be defeated by it. Though, after returning from the battle, the Thirteen Heroes kept silent about what really happened to the "God Dragon," and the truth remained a secret.

The Undead King Arc
Upon witnessing the unbelievable powers of Ainz Ooal Gown and Albedo, Nigun Grid Luin accused the two of being Evil Deities.

The Sealed Evil Tree Arc
Pinison Pol Perlia vaguely mentioned a group of powerful monsters that nearly destroyed the world. According to her, one of these monsters hid in the Great Forest of Tob.

The Invaders of the Large Tomb Arc
When the workers from the Baharuth Empire began to explore the surface of the Great Tomb of Nazarick, they theorized it to be a ruin from a time before the rampage of the Evil Deities.

The Craftsman of Dwarf Arc
Gondo Firebeard recalls the fact that when the Evil Deities was still present, the last remaining royals left the Dwarf Kingdom to join the battle against them. It was noted that the city of Feo Berkana had been abandoned during the attack of the Evil Deities two hundred years ago. After the Demon Gods had rampaged through the Royal Capital, only one member of the Dwarven royal family was able to stay alive after all the ordeal he went through to survive. He was none other than Magic Craftsman, the last king of the Dwarves who later part ways with his homeland, taking along almost all the national treasures to readily combat the Evil Deities. In the end, Ainz is able to learn that most of the information and documents regarding Runecraft was destroyed thanks to the efforts of the Evil Deities.

The Paladin of the Holy Kingdom Arc
When Jaldabaoth attacked the Holy Kingdom, Kelart Custodio estimated his power to be greater than that of the Evil Deities.

Strength
Evil Deities were extremely powerful according to the New World's standards, requiring the Thirteen Heroes to face and destroy each of them one by one. While at the same time, it seems apparent that the Evil Deities were not all equally powerful as they've been defeated in different ways.

However, most of them, if not all, did not exceed level 60. Some may have been weaker, as stated by the Nigun Grid Luin of the Sunlight Scripture that one such Evil Deity was actually slain by the Dominion Authority and its 7th tier attack spell "Holy Smite", which according to Ainz, is weak.

In the Web Novel, it seems the Evil Deities are capable of using 7th tier spells.

Trivia

 * In the Web Novel, it is hinted that the Evil Deities were beings that once served under the Six Great Gods.
 * The battle against the Evil Deities was one that transcended the racial barrier among the Thirteen Heroes.
 * According to Nigun of the Sunlight Scripture, he has heard that the Thirteen Heroes had defeated and sealed away the Evil Deities, implying that not all of them are completely wipe out for good.
 * It is speculated that Zy'tl Q'ae might be one of these Evil Deities sealed away.