Nekron

History
Nekron is the pure incarnation of Death, who rules the dead universe of Ryut. Ryut lies in the void of creation, preventing Nekron from passing into the mortal world.

In order to prevent Nekron from passing into the Multiverse, the Presence fractured Nekron into numerous pillars to splinter his power. These include, Death the Endless, the New God Black Racer, and the Olympian Hades.

War on Earth
On Earth, a Lord of Chaos named Eclipso becomes an apostle of Nekron. Eclipso amasses an army to storm the House of Heroes, where he will attempt to destroy the indestructible White Lantern. Destruction of the Lantern would "potentially" allow Nekron to pass into the mortal world, as well as the extinction of all life in the universe.

Nekron imbues Eclipso with a portion of his power, allowing him to kill the Lord of Order, Nabu. Eclipso eventually fails to destroy the White Lantern, causing Nekron to lie dormant for millennia.