Needs a picture of Marduk, of Jadugarr, all probably with a caption of a quote from the game.
The Cult of Ashur was a new belief system that arose in the world of Sacrifice not long after Eldred's arrival, opposing the traditional five god pantheon. Its mundane leader was Jadugarr and its divine leader was Marduk.
The Initial Emergence
After Mithras foretold his prophecy, the gods began warring with each other again. The common people, tired of the wars, turned to this magical entity, who they had only known as Ashur, to provide them with another way - and to finally bring an end to the wars between the gods, once and for all, by toppling the gods themselves.
Ashur is, in fact, the demon Marduk, who had already destroyed the protagonist Eldred's homeworld and, like Eldred, has come to the world of Sacrifice, intending to destroy it next. However, his true identity is unknown to the majority of the populace, who perceive him as a possible savior.
The First Downfall and Reemergence
At first, the Cult's actions consisted of nothing more but apocalyptic preachings by Jadugarr across Glebe and Elysium. However, after garnering attention from the gods, who decided to eradicate the Cult, this passive attitude would change. The aftermath was obvious - people were intrigued by Jadugarr's words, but he was banished, and seeing as how he lacked a patron god, presumed dead (although Zyzyx implies that Ashur might have other altars).
With the war between the gods spreading like wildfire, resulting even with the death of one of them by the hands of Eldred, the Cult needed no actions to be done. The people were despairing and chaos spread in the realm of the fallen god. In fact, using the ensuing chaos and the element of surprise, the Cult began their war with the gods fairly late in the campaign, but their actions had dire repercussions. Their attacks always had the death of a god as a result (except for Stratos), irrelevant of the god Eldred was following. They coordinated their attacks in such a way to avoid targeting the gods Eldred was employed to slay, maximizing the damage done to the traditional five god pantheon.
The Final Downfall
As the End Days were on the world's doorstep, the Cult had worldwide following. They allied themselves with the Servants, Marduk himself pledging allegiance to Stratos, with no real sincerity behind his words. As such, their last actions consisted of either defending Thryhring from Eldred or busy slaying yet another god. If it came to pass that they were opposing Eldred, their failure was certain, but still at a great cost to the general moral, and most likely a death of another god that Marduk slew himself.
With only one god standing not toppled by the war combined with the actions of the Cult, Eldred sought out Marduk's source of power and had a final confrontation with the demon. Following Marduk's death, the Cult was left without its claim on divine worship, dispersing much like the followers of slain gods. Any remnants of it, including the wizards who might have served the Cult, were probably subjugated by the one remaining god and his forces.
Jadugarr, the rogue elementalist, is one of the first followers of Ashur. After his fellow centaurs had been exterminated (under circumstances not explained in the campaign), Jadugarr abandoned Stratos and since then, he's been seeking revenge against all the gods. He found a way to do that in Golgotha, by summoning Marduk. The mandate for protection of the Demon Gate from Charnel's Minions at that time belonged to Stratos, who not only did not stop the ritual but also oversaw it and used Jadugarr's summoning as a part of his plan to destroy his competition.
In James' third mission, Jadugarr explains to Eldred that he would sooner see a mortal rule the world than a divine, as a bad mortal would at least pass away sooner or later. He is already willing to fight against the gods, no matter the consequences, and finishes with an ominous sentence that sums up the sentiments of the people: "The people are ready to abandon these gods. All they need is something else to believe in." In Persephone's fourth mission, Eldred confronts him, warning him that Ashur is in fact Marduk, destroyer of worlds. Jadugarr replies cynically: "[...]I will see these unjust gods thrown down if I must bargain with the Angel of Death to do it."
Hachimen is the only other known wizard in the service of Ashur. He has joined Ashur only later during the war, although when exactly is unknown. Hachimen's reasons for joining the Cult are unknown. It is possible that, being a mercenary, Marduk had simply hired him to serve his ends; however, he could also have joined out of principle. Either way, later during the campaign he is shown to be truly devoted to Ashur, taunting Eldred with exclamations such as: "The gods have no future!" Hachimen definitely is serving Ashur by the eighth mission, as sorcerers of Pyro will meet him in Idylliac; he is also the most likely opponent in the ninth mission.
The Cult of Ashur starts to become very popular during the war even among the common people. Starting from the eighth mission, idols to Ashur start to appear throughout the land, even in the capitals of gods' realms. Many commoners surround these idols each time, worshipping Ashur.
By the final mission Marduk has accumulated allies from all realms and used them primarily as guards to his source of power - the Megalith on Crucible Island. They were mostly level 6 to 9 creatures, ranging from artillery units to titans.
Gods' Views on the Cult
- "Go as an envoy to Pyro and offer mercy and forgiveness if he will join us in battle against Marduk. Else he needs share Charnel's fate. This do We proclaim is Our justice." – Persephone, No Mercy (Intermission)
Persephone, while not considering the Cult to be as great a threat as some of her traditional enemies, is interested in learning about it even before Eldred's revelation of the actual power behind the Cult. After that, she views it as a threat and uses it as a pretext to have the Demon Gate destroyed, to prevent Marduk from summoning more demons into the world of Sacrifice. She then uses the pretext of unity as a justification to slay the other gods should they refuse to side with her.
- "It's the prophecy what's got everyone so worked up. Well, before we go off half-cocked, it's probably best to look into them forces of destruction a little closer. I think I know the way." – James, Balance of Power (Intermission)
James is the first one to take an interest in Jadugarr's actions that led to the formation of the Cult. Even after Eldred's revelation, he is more worried about his traditional foes, particularly Pyro. He is latter deceived by Marduk himself, disguised as the seer Mithras, into believing that Charnel is behind Marduk's summoning. By the coming of the End Days, James commands his geomancers to search for Marduk, while Eldred defends the Glebe.
- "That is a lie. Marduk was summoned by that centaur. I merely took advantage of it." – Stratos, The End Days (Intermission)
Stratos is the only god to directly benefit from the actions of the Cult. He uses the Cult, particularly through Jadugarr, to cause the demise of other gods. Depending on how the campaign was played, this often backfired on him, he himself being destroyed by either Jadugarr or Marduk, miscalculating the power of the Cult and of the demon behind it.
- "The demon? A demon destroys, but it cannot build. Thus even as an enemy, it is my ally." – Pyro, No Mercy (Persephone)
Pyro is the one who cares the least about the Cult. Unlike his other foes, he doesn't even view it as worthy of destruction and thinks of it as actually favorable to him, as fighting the demon made him stronger. Should Pyro remain the only god, unlike the other gods, he will offer Eldred no incentive at all to go after the Cult, making Eldred take matters into his own hands to see things through by destroying the Cult himself.
- The indignity! James actually suggested that this upstart, this Ashur could be a greater threat than the God of Slaughter! – Charnel, Shadow of the Past (Intermission)
Charnel is the god who is most ardent about eradicating the Cult. He views the cult as a personal insult to his prestige. After Eldred's revelation, he decides to summon a new demon to fight Marduk. While that most likely wasn't the primary reason for the summoning, it is revealed in one of the possible scenarios that the demon was slain by Jadugarr, meaning it really was used to hunt down the cultists.