Doom
The granddaddy of the first person shooter, the original ass-kicking demon-slaying 3d slaughterfest, Doom is a franchise that demands respect even in the hallowed halls of /tg/.
Minimalistic in plot, Doom is easy to grasp; you are a Space Marine (no, not the 40K guy, a jumped-up soldier who is sent to fight on other planets, so closer to the Imperial Guard) stationed on Mars. Somehow, demons break through into our reality and slaughter everyone else on the planet. Your job? Fight your way to where, you hope, there's a ride off of this rock, and make bloody mincemeat out of everything standing between you and salvation. Standing in your way are armies of zombified fellow marines and eggheads, fireball-tossing imps, hulking flesh-eating demons, cyborg-demon monstrosities, and various other hell-spawned nasties who want to kill you horribly. Good luck. You'll need it...
Although not the very first of the FPS genre (that goes to its predecessor, Wolfenstein 3D), Doom was definitive to the genre, so much so that "Doom Clone" was the standard nickname for many years afterwards. And, for the time, it was incredibly dark and gory. To put it in perspective, there's still people playing it and hacking around with the source codes for it to make funner games to play - there's even a monstergirls modhack being churned out, complete with hand-drawn artscenes and a complete revision from "kill the demons" to "fuck the demons into submission". Hell, Final Doom is a compilation of maps made by two out-of-company designers made just because they could in the 90's!
Adaptations
Vidya
The original Doom was fast-paced and bloody, but not afraid to take breaks for scares, either; there's some really creepy levels in there. Doom II, meanwhile, was even faster-paced, a circle-strafing explosion-rich gorefest that defined the game and the FPS genre in the eyes of its fandom. Plot was bare-minimum: Demons took over Phobos and ate Deimos, kill them all. Or, in Doom 2's case, Demons are trying to infest Earth in revenge, kill them all AGAIN. There were some other adaptations, an N64 port that played up the scary and Final Doom for the PS1 which had a bunch of fan maps.
In the early 2000s, Doom 3 came along, following in the example of Doom 64 (a little-remembered Doom game on the Ninendo 64) as a slower-paced, creepy, almost Survival Horror themed game. It's not a bad game, but it's not the same action-packed thriller that people were expecting from Doom II, and so while there was an expansion pack/semi-sequel in "Resurrection of Evil", Doom eventually went back into obscurity. The plot tries to be a bit deeper, with this prophecy about an alien weapon capable of killing the denizens of Hell, while RoE had an unethical scientist trying to get his hands on an unholy artifact while the new PC tries to keep it out of Hell's hands.
Then the latest Doom came out in May 2016. This rendition can basically be described as "3d Brutal Doom II", with features like ripping enemies apart with your bare hands and having to stay on the move to avoid being torn to shreds. The plot is also about as bare minimum as the original, kicking the player straight into the action with waking up on Mars, immediately smashing a zombie’s skull, and basically being told “demonic invasion, go kill everything.” Also, the player happens to be waking up chained to an operating table/ritual alter (and proceeds to break the chains), heavily implying that this Doomguy is a demonically superpowered badass specifically created to counter said demonic invasion.
Comic
The only thing you need to know about it is that it's a masterpiece of absurdity and comedy that only the 90's could make. Sure, it's only one issue that was released back in the days of the first games, but it was just that fucking STUPID that you need to see it to believe it!
Board Game
Yes, there is a Board Game, thus giving the vague '/tg/ related' qualifications this site uses. It was released around the time Doom 3 was released, though it wasn't that remarkable and is pretty hard to find nowasays.
Movie
Also (roughly) around the same time as Doom 3 was a movie starring Karl Urban and former WWE superstar Dwayne "The Rock" Johnson. It pretty much replaced the whole Hell plot with some genetic experimentation to give people superpowers that inevitably goes awry, and a squad of Marines sent to investigate the mayhem. It wasn't that good, with the only really 'good' scene being this one scene where it's all FPS-style like the original games and has monster killing.