Triumvirism

Triumvirism is the worship of the three core deities, Penance, Cognance, and Sigil: the Triumvirate. This religion is most ardently practiced in the Requiem province. The three gods each represent an aspect of morality; lawful, neutral, and chaotic.

• Cognance. The Neutral goddess; she represents aspects of the 'mind' and is revered by scholars, monks, and several domains of clerics like arcana, knowledge, and forge. Her symbol is an unbroken circle; also represented as a sun, a shield, or a lake
• Sigil. The Lawful god; he represents aspects of the 'body' and is the patron of most paladins and war, order, and death domain clerics. His symbol is a solid square; also represented as a plate armor chest piece, four interconnected swords, or a castle
• Penance. The Chaotic goddess; she represents aspects of the 'soul' and is followed by life, tempest, and trickery domain clerics as well as some druids, paladins of the old great ones, and even some warlocks (through so-called intermediaries) her symbol is an upside-down triangle; also represented as a spear tip, a mountain peak, or a crown

Triumvirism derives its origins from the philosophical movement that saw the decline of the Antecean Pantheon. When Antecean scholars learned that deities draw their strength from devotion, there was a sort of secular revelation that true divine power is instead drawn from mortal people; an amalgamation of their body, mind, and soul.
After the fall of Antecea, the concept remained, but as time went on, its origins became murkier and murkier. Eventually, the religion saw an explosive resurgence starting in Requiem when humanity began reconstruction. A man named Eero Hengellen claimed to be the reincarnation of an avatar of the three deities who ultimately stopped whatever onslaught destroyed Antecea before it could fully eradicate humanity. He gained a substantial following, and in the short few decades of his ministry, his following went from a fringe cult to a prominent religion. In addition to being a prolific profit, Hengellen proved to be a cunning warlord and united the tiny, disparate kingdoms of men that had formed following Antecea's fall. He promised them a new, united Requiem and led them to reclaiming the city that would become Sigil. While he would not live to see his ambitions fulfilled, his sons took up the mantle and brought the other two major cities of Requiem under their banner and their beliefs. Their movement gained greater validation when the sons proclaimed that they had found the reincarnation of their father among their people.
Ever since, the Church of the Triumvirate has been led by a "reincarnation" of the Avatar, called the Orator, who the grand priests of the church seek out whenever the previous perishes. This has been the way since the beginning, up until roughly 30 years ago when the previous Orator died and a new one was nowhere to be found. In the absence, a middling cleric stepped up, claiming he received visions from the gods themselves commanding him to take up the mantle. The clergy rejected his claims, but ultimately, he found support in the city of Penance, who had become dissatisfied with their current monarch. Eventually, this so-called "pretender" was granted the office of Orator and King of Penance by the city. Outside of Penance, the Triumvirate vehemently denies the legitimacy of this "False Orator" and continues their search for the true Orator, which they finally concluded with the discovery of Zandre Rama, who was part of an adventuring group that saved Requiem from the Reckoning. Unfortunately, Zandre's essence was marked with a dark presence, and so long as that presence remained, he would not be able to fully take up the mantle of Orator.

As of 1590

After the Extinction War, Triumvirism faced an internal schism brought about by the "progressive" ideas of their then-Orator Zandre Rama. Unlike his predecessors, Zandre was not brought into the folds of the Church until he was well into his adulthood, owing to a curse inflicted upon his family by The Heralds of Aevilok who sought to destabilize the Church. Because of this, his worldview and opinions on the church were highly colored against organized religion, and so he took up a campaign of reductionism and decentralization. To his surprise, his movement found acceptance within some branches of the Church. To his complete lack of surprise, there was also great resistance. 
What followed was several decades of infighting wherein two major factions broke out: one favoring the traditional mission of the Church, and one following Zandre's principles. Unfortunately for the former, the fundamentalist faction was co-opted by zealots and extremists, primarily from Penance, who wished to see the Church overthrow the new Haedian Empire and replace it with an Oligarchy. This led into the civil troubles that plagued the Empire for some time after the Collision, and ultimately resulted in the Fundamentalist movement being squashed along with the Penance insurrectionist movement. 
Since then, the Church has receded in influence, being supplanted by Aonism in Haedia by the mid 1300s. Only Borne remained as a fully Triumvirate state.
Recently, a neo-fundamentalist group has gained traction in The Talhani Isles thanks to their colony of Hengellen. For now, it remains unclear if this new movement will turn out as violent as their predecessors, or if they merely wish to return to a philosophy long-forgotten by time.

Eero Hengellen

Hengellen was born some time in the late 200s in the Champion's Plain near a settlement that would one day become Borne. Hengellen was fiercely curious about the nature of the cosmos and spirituality. In that time, mankind had devolved into worshipping a smattering of different pantheons and deities, but Hengellen never felt drawn to any particular one.
He spent many days of his youth wandering the ruins of an Antecean structure on a hill overlooking the confluence of two rivers. On one such expedition, he discovered a previously obscured entrance to a subterranean chamber. It was here that he experienced a life-changing vision: A trio of ethereal figures came to him and proclaimed him the reincarnation of their champion who fended off the doom that took Antecea; saving the rest of humanity from complete extinction. They bid him reunite the lands of Requiem in the Trio's name. Thus began the campaign to unite what would come to be known as The 1st Haedian Empire .
Over the years, Hengellen would return to this site often to commune with the Trio. He would record his visions, conversations, and musings in a tome that would go on to be the basis of modern Triumvirism: the Sacred Transcriptions.
The Transcriptions were added to by subsequent Orators following Hengellen's death. Indeed, the Sacred Transcriptions are one of the few holy documents that still goes through revisions and new additions as Orator's continue to commune with the Trio in those old caverns.