Raiders

Raiders are any group of people who pillage, plunder, murder, or otherwise ruin the day of anyone unfortunate enough to not be one of them. If there were still laws, they'd be outlaws. Raiders tend to organize into loose confederations of gangs in the post-apocalyptic wasteland and are a constant problem, because it's much easier for them to just shoot people for their money, food, and other valuables than to earn a living. Raiders typically prey upon travelers and very small towns, leaving more populous areas alone, where they are outnumbered and have no element of surprise.

There are three distinct raider groups referenced by the first Fallout: Jackals, Vipers, and Khans, although only the latter appear in the actual game. All three groups originated from Vault 15. Quoted from the Fallout Bible:
 * The Jackals: The first clan, the Jackals, is your typical group of crazies. They have no morals except one: survival. They use group tactics to overmatch their enemies. They are craven cowards, though, and will not attack unless they know they can win. They band together in their hideaway and fight over the spoils.
 * The Vipers: The second clan, the Vipers, are mysterious followers of an ancient religion (or so they claim). They usually only come out at night to hunt for food or to conduct raids. They are very ruthless when it comes to combat. They prefer stealth to strength. They usually carry bone knives dipped in Pit Viper venom. This poison, when in the blood stream, paralyzes the victim. Most victims captured in this way are taken back to their hideout.
 * The Khans: The last group, the Khans, is probably the most dangerous. They live the lifestyles of Mongol warriors, raiding towns, burning what they cannot take and capturing the survivors for use as slaves. They usually travel in small scouting bands, but sometimes they roam as full war parties. The Khans above all else respect strength. They are eager in combat to prove their worthiness to the clan by engaging in hand to hand combat with fists or clubs. The Khans carry very few firearms (since they are for cowards). Anyone showing superior strength is worthy of their respect. The leader of the Khans is so because no one has beaten him in combat....yet.

There are numerous other groups of raiders in Fallout 2, among these are the cave-dwelling raiders somewhere North of Broken Hills, protected by raised plates, falling traps and barbed wire-walls with locked and trapped doors. They are actually hired by the Bishop family of New Reno with arms supplied by the New California Republic to lay pressure on Vault City to force them into becoming annexed by the NCR. Or so they hope to achieve...they're actually more like mercenaries, but in the eyes of Vault City, they are raiders, only more tactical: Never going through a line of fire, having officers, and laying supression fire on important targets. It seems as if they have no weaknesses, except for a hidden back-exit they are supposed to use in case of retreat. There is also an alternative entrance. The New Khans, led by the only survivor of the original group, also appear in the second game. They are hiding out inside the secretive corridors of the ruined Vault 15, protected by squatters.

Fallout 3
The Raiders in Fallout 3 are mostly hostile, lawless, anarchistic, criminally insane humans who live out in the wastes of the Washington D.C. area. You can expect to encounter them more often at lower levels and they are usually armed with a fairly wide range of weaponry. They often carry pistols (.32, 10mm, and Chinese), combat shotguns, and hunting rifles, as well as melee weapons and grenades. At higher levels, they sometimes begin to carry assault rifles, SMG's and even some of the big guns like the missile launcher and flamer. They can occasionally be found hunting with guard dogs as well. All Raiders wear some form of Raider armor. All Raiders have sunburnted skin, which seems to be unique to the Raider faction.

Raiders seem to vary in level, often indicated by the weapon they carry. Low-level Raiders armed with pistols actually seem weaker than Vault 101 Security, whereas higher-level Raiders carrying assault rifles or heavy weapons are noticeably more durable (although still of average human durability). Regardless, Raiders are often poorly armored and tend to die quickly with a few well placed shots - making them only a moderate threat in small numbers, however when encountered in larger groups Raiders can be deadly efficient and should be approached with extreme caution.

Known locations of Raiders in Fallout 3 are Springvale Elementary, Evergreen Mills, Cliffside Cavern, Dupont Circle Station, MDPL Mass Relay Station, Chaste Acres Dairy Farm,  Friendship Heights and Super Duper Mart. Also in the Bethesda Ruins there is a larger-sized band of Raiders. They can also be found roaming around the Capital Wasteland. Raiders also inhabit Wheaton Armory, VAPL-84 Power Station, Scrapyard, Dupont Northeast and Kaelyn's Bed & Breakfast and all of them respawn with different weaponry every day or two. Raiders are also frequently found combatting Super Mutants throughout downtown D.C. This comes in handy when the Player gains the Lawbringer perk. They also come in handy when fighting super mutants, where the raiders will focus on killing the mutant first, instead of going directly for the Lone Wanderer (the PC).

The largest band of Raiders is at Evergreen Mills, where there are at least 20-30 raiders, but also a Super Mutant Behemoth. There is also a "bazzar", or trading center within the actual mil. The only person you will be able to trade with is Smiling Jack, who carries the unique Terrible Shotgun.

Raider locations tend to be marked with spray-painted symbols and mutilated bodies hung up with meat hooks on chains.

Raiders have no alliances with other factions and will attack everyone but other raiders. They appear to be quite cruel, as places they inhabit are usually filled with the mutilated bodies of other raiders and wastlanders, implying that they torture captured enemies. The Raider Sadist Armor is equipped with several dismembered hands that the raider has kept as trophies.

Raiders can become allies by using the Mesmetron to daze them and then attaching a Slave Collar to their neck. If your Explosives skill is high enough, you can remove the Slave Collar from around their neck at the raider's request and he/she will then be allied to the player character. The allied raider will even kill other raiders following this action.

Raider Hazing
In Fallout 3, you may come across a random occurrence of a raider hazing ritual. Four raiders surround a fifth raider initiate standing in his underwear (no armor), each taking a turn in beating him with a melee weapon. The dialogue suggests that he has to take and accept the pain he is receiving. The raider group is close enough together that they can all (or mostly) be taken out by a frag grenade aimed at the raider initiate.

Burning Wastelander
Sometimes you can encounter a raider armed with Flamer hunting a wastelander.

Raider In Tesla Armour
You might encounter an unarmed Enclave officer, normally dressed and an Enclave soldier without armor. If you kill these two, Three raiders attack, and one of them is wearing Telsa Armour with An eyebot helmet.

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