Eight Greed Kings

Eight Greed Kings (八欲王) were legendary figures in the New World, who appeared five hundred years ago and conquered the world with incredible power.

Background
Five hundred years ago, the Eight Greed Kings appeared and sought to conquer the whole world. However, their rule was almost immediately short-lived due to an internal conflict which led them to self-destruction. Nowadays, most of the things they've constructed were literally destroyed, leaving only ancient ruins for what was once made up their civilization. The only city left standing is under their floating castle, Eryuentiu. The Eight Greed Kings are said to be one of the few besides the Six Great Gods, who increasingly spread the existence of Rank Magic further into the New World.

After their downfall, the Platinum Dragon Lord took on the task of guarding their magic items to ensure no one would ever be able to misuse them.

The Men in the Kingdom Arc
Evileye brought up the legend of the Eight Greed Kings while talking with Climb and Gagaran.

Strength
The Eight Greed Kings were known to be immensely powerful, as they had slain most of the Dragon Lords in battle. What the Eight Greed Kings left behind are the Eight Great Weapons wielded by them, including their guild weapon (a sword). Evileye mentioned that their item "Nameless Book of Spells" was worth the price of a single world, so it may possibly be a World Class Item. The floating castle, Eryuentiu was a city guarded by thirty guards equipped with very powerful magical weapons. Fluder stated that if he had a magic item from the Eight Greed Kings, he was certain that his Magic skills would rise by another level. As they should never fall into the wrong hands of others, the weapons are not allowed to be taken from there. The only exceptions being the few items the Thirteen Heroes were permitted to take with them.

Trivia

 * Eight Greed Kings are the second group of YGGDRASIL players to be transported to the New World after the Six Great Gods and before the two players of the Thirteen Heroes.
 * In the Web Novel, it is certain that they are YGGDRASIL players, as their city produces items which only exist on Earth, like a suit or a katana, and they owned a guild weapon.
 * It is also confirmed that they can revive after death, though they become weaker and weaker after repeating the revival. This might be due to the revival penalty of YGGDRASIL.
 * It's stated that if the Eight Greed Kings had not attempted to dominate the world, humanity would have already been annihilated by the stronger races.
 * It has taken about a number of ten Dragon Lords to defeat one member of the Eight Greed Kings.
 * Brain Unglaus got his hands in obtaining a katana from their city.