There are few things that will persist for as long as humanity lives. Everything is ultimately transient, save the ills of humanity that exist near universally. Of course, Zack had no reason to know this, but they would soon become all too familiar with the concepts.

Zack was born in the upscale neighborhoods outside of Los Angeles, to a family of rather well-off folk. The stock of which granted them no extraordinary childhood, although they were notably frailer than the average human, it wasn't their care to begin with. They always had a magnetic attraction to the truth, or rather the allure of revealing conspiracy. Most of their upbringing, this lead to nothing but wild theories about the local high-school administration, although it would spur them to find their calling in college: Journalism.

Life in college was a far cry from what they had experienced before. Going to Loyola-Marymount was surely an interesting experience, as Zack was most definitely not a Jesuit, but it held an allure that Zack couldn't quite place. It was only natural that once they actually arrived at the College, they heard rumors. A secret fraternity that held only the elite, preforming odd rituals at the dead of night on a campus below the main hall. It was simply too conspiratorial for Zack to ignore, and as such they pursued the rumor.

Like any good conspiracy, Zack knew it had to be rooted in truth. Days of casual searching turned up a checkbook trail, a discrepancy in college finances that didn't quite add up, suggesting an extra expense that didn't appear on any ledgermain. They nearly had it, with a bit more searching they would soon find the core truth of this conspiracy.

The fraternity did indeed exist, and Zack was invited...it appeared their investigation was noticed. However, Zack was not investigating to join, but to expose the group. Either way, it wasn't as simple as showing up to the next meeting, they had to be...filtered. Zack assumed this was some more-extreme hazing, or maybe a LARP. Zack was always made to interact with faceless figures hidden beneath ushered green cloaks, packages showing up at geocaches. They were made to ingest substances, odd ones, rather illicit at that-not that it was all that different from what they normally did at Loyola anyway-and be innoculated against diseases they never heard of. Part of Zack knew that they were in over their head...but that part was silenced by the slow indoctrination they were being subjected to.

The figures spoke of the end of times, of four figures that would usher them all into the realms beyond, of a wasteland located at the end of time and space, where God threw all of His mistakes. It was this group that would herald the gods, and claim there rightful place in this wasteland: Abaddon. It seemed all so biblical, prophetic, and the more they earned the Fraternity's trust, Zack was privy to things beyond the mere plane of reality. They knew now: Those figures in cloaks weren't mortal...weren't human. They had become something more. Maybe it was a curiosity, maybe it was the deep-down lust for power, but Zack knew that there wasn't any turning back. As the weeks turned to months turned to a year, Zack fell further, until it was time for his final initiation.

They had received their own green cloak, although they had no extraordinary presence of their own. It was a late night, just before the summer solstice. Nobody knew where Zack was going to be that night, so it was perfect. In the annals of the school halls, deep below the surface, Zack had been called to preform the induction. There were so many figures, packed around a pit...filled with the corpses of animals and beings that defied logic too look at. The air was filled with the clamor of chanting and conversation, all the while a subtle droning played over the crowd.

Zack was brought along with several other people to the edge of the pit, and unhooded before the crowd. They saw classmates, teachers, those they didn't recognize. They barely had time, before they were shoved in the pit and made to steep in the filth, brutally assaulted by the other hooded figures.

Soon, all within the pit fell silent. The time of reckoning was at hand. Zack held on to life by a thread, unable to move for the broken bone and ripped flesh that came to be their body. Minutes passed in silence, hours, before a new noise supplanted the soft sobbing of the victims. It was an infernal buzzing, rising from the once-dead corpses to become something worse and greater than any mortal man.

The next morning, residents of Loyola Marymount awoke to friends and teachers missing, without a trace to be found. They had all seemingly up and vanished, with only one consistency between all accounts of the morning after. The stench of rot was thick in the air, and there was an odd buzzing.

TLDR:

Zack liked conspiracies as a kid, goes to Loyola Marymount for a Journalism degree. Once there, they find out that a secret fraternity exists, and investigates it. They end up joining and get indoctrinated into a cult, then get sacrificed ritualistically but kill the entire cult and escape. Thereafter, they live and try to soothe their own disease, having become a champion of the Horsemen.