Hagal

Emperor of the Yungadar​

Hagal is an ascended god who attained godhood by creating the seed of a religious god in his image and ascending to merge with it. He is rather young for a deity, only a few centuries old, but as a human was old enough to have lived through the death of the Emperor, which is what unlocked his psychic powers, of which daemonology was his specialty.

Polity
Hagal is the leader of the empire known simply as the Yungadar. All its citizens, Hagal's worshipper base, pledge their souls to Hagal, who will consume them after they die. Depending on who the person is, they go along with this for one of two reasons (or a mix of both).
The first reason is simple pragmatism. The people of the Yungadar believe that after they die, their souls go to the Warp, where they will become the food and plaything of daemons for potentially all of eternity. It's a fate that no one wants. The idea of dying after one dies isn't that bad if raised to think that way, and when compared to the alternative it's akin to salvation.
The other reason is idealism. Many people believe in the righteousness of their soul being consumed by Hagal, whether it be in thanks to the man who protects them, enabling the survival of their fellow Yungadir, or to act in service to Hagal's higher goals.

Goal
Hagal, in his capacity as a human and as the Emperor of the Yungadar, has declared war on the Chaos Gods and intends to defeat them, driving them from the galaxy forever. He's survived so far for three primary reasons. First, he lives in an age where the gods face far more threats of greater power than they ever have before, and while they despise him on principal have higher things on their priority list. Second, he's fairly young, and has yet to have rolled the dice of fate too many times as of yet, relatively speaking. Third, with his original mortal body as his avatar, he is incarnated into the Materium, where the Chaos Gods have immeasurably less power than in the Immaterium.

Hagal's Runes and Rune Brethren
The most powerful of the Yungadar's psykers undergo a ritual wherein they become host to a minor divine servitor of Hagal's. These psykers are known as Rune Brethren, named as such for the rune of Hagal that appears somewhere on their soul after they binding. The rune is in fact the divine servitor itself. The servitor is inert until the psyker dies, at which point it ensures the soul goes to Hagal. In addition to sending their souls to him, the divine servitors also bind their souls to Hagal, which provides a number of positive effects. One of the effects is resistance to the corrupting power of Chaos, which is a constant threat to those gifted with psychic talents. It also provides the same effects as the soul binding of the Imperium's astropaths. Because of this, compared to other polities, the Yungadar's astropaths are superior and their psykers are more stable.

Given a piece of the Yungadir emperor himself and trained by either fellow Rune Brethren or Hagal himself, the Rune Brethren are elite psykers and one of the Yungadar's trump cards. Whether they end up being battle psykers or sanctionites, Rune Brethren play important roles within the polity that gives it the crucial strength to survive the Time of Ending.

While Hagal's rune is the first and most important of all the runes a Rune Brethren receives, Hagal is capable of giving out different types of runes to those of the Rune Brethren who earn his favour. Hagal originally didn't have access to any of these runes, instead crafting them over the course of his life after becoming a divinity. The means by which he does so is by taking a Rune Brethren who shows truly exceptional natural talent in one psychic area, from anything as broad as a psychic discipline to as narrow as a specific power, and stripping their soul of everything but the part that held that talent. He then transforms that talented section of the soul into a Master Rune, one of Hagal's Living Saints, and incorporates it into his own being, thus gaining the talent himself. Thereafter, he can provide less potent versions of the Master Runes to his Rune Brethren.