If you've played the game, you've most naturally seen the in-game intro sequence which summarizes the story as thus: a strike team known as the HUNT is sent to San Nicolas Island to scope out a bunch of weirdos inhabiting the island's monastery. Before they can report back to their HQ, their boat is exploded, forcing them to enter the ancient site of worship.
It's the manual that explains a bit more of the things we're familiar with now:
So this is where we learn about the Oscurido cult that worships El Oscuro and wishes to blast Los Angeles to kingdom come for bad guy purposes. However, one thing always puzzled me: the mention of "a pyrotechnics expert and a rich movie studio head have joined forces with the Oscurido cult." What's that all that about?
Strictly speaking, the manual does plainly, if not indirectly, identify who these two individuals are supposed to be:
So if you were ever curious, "General" Darian is not actually a general. He's just a special effects guy. And Sebastian Krist is not a man of military rank either. He's the former head of a movie studio. That studio was called "Triad Pictures".
Technically, everything I've stated here so far has always been easily accessible information for anyone who checked the manual, although I don't think many people acknowledge the fact that half the bosses in the game are filmmakers. Still, what the hell is "Triad Pictures"? Where does San Nicolas Island fit into the picture? What does a man with a lunchbox obsession and Joe sitting in a chair threatening to staple his own hands have to do with Tom Hall wearing a robe? Why does the HUNT blow up an innocent and defenseless tower at the end of the game? Believe or not, there are answers to all of these questions, and as far as I can tell, they were only revealed within the Player's Guide story synopsis and no where else.
Rather than provide a scan, I'm just going to retype the whole section:
Rise of the Triad Official Players Guide said:
Triad Pictures, owned and run by Sebastian Krist, has long been suspected as a haven for the cult worshippers of "El Oscuro, the Dark." The Oscuridos believe their divine godhead will come and cleanse the world of non-believers. Their rituals are rumored to include animal sacrifices, pagan "black magic" ceremonies, and other grisly satanic events.
Krist has masterminded a number of weapons heists and tapped the expertise of John Darian, a special-effects wizard, to kill his Hollywood rivals. Now the pair and their followers have retreated to an old Spanish monastery on San Nicolas Island, a secluded hunk of rock that's situated about 20 miles west of Los Angeles and partially owned by Triad Pictures.
Even though there isn't enough evidence to directly link Krist with the Oscuro cult, a special team of counter-terrorist agents, organized with the cooperation of major world powers under the United Nations and called the HUNT (High-risk United Nations Taskforce), has been trailing Krist and observing activity on the island. In the last few days, monk cultists and guards wearing uniforms with the Triad Pictures logo have been spotted overseeing the movement of a shipment of explosives off the island. The HUNT has also discovered that the cult plans to destroy Los Angeles. In fact, the bombs planted around the city have already begun to detonate, but before the HUNT can leave the island or even get to a radio transmitter, the cultists destroy their boat. Left with no way out, this lightly-armed band of commandos decide to fight their way into the monastery and destroy the remaining detonation devices before Krist and Darian can wreak havoc on an unsuspecting city. Millions of lives hang in the balance. You're a member of the HUNT team. If you succeed, you'll be a hero to billions. And just think of the movie offers...
MISSION OBJECTIVE
Kill or be killed. This simple statement encompasses a number of more complicated tasks, like solving puzzles, killing Triad members, finding weapons, killing monks, getting ammunition, slaughtering more followers of El Oscuro, and finding power-ups and life restoratives.
The overall goal of the game is to locate Darian, Krist, and El Oscuro's earthly manifestation, and then rid the world of their odious presence. They guard the detonator device that is systematically blowing up explosives hidden all over Los Angeles. Destroy this device, win the game, and you may earn a few weeks of leave before your next mission.
And there you have it. Everything about the game makes sense now. The ancient monastery was renovated by Triad Pictures to be used as a movie set, a cover for their true nefarious deeds. The triad logo and even the "Triad" name itself alludes to the cinematic production company owned by movie mogul Sebastian Krist, John Darian being the head of the special effect department. The thing you blow up at the end of the game is a "detonation device" that would have blowed up Los Angeles (or rather, you stopped it from further blowing up the city, it seems). And that truly is some miscellaneous knowledge.
For the record, I don't think the 2013 remake utilized much of this movie production studio/filmmaker espionage aspect of the Triad storyline.