Dark Brotherhood

The Dark Brotherhood is an organization of highly trained assassins who carry out assassination contracts. The Dark Brotherhood is called upon by those who wish to utilize their deadly services through a ritual called "The Black Sacrament". They were once the most feared organisation in all of Tamriel, but have lost their reputation over time. At one point, they were governed by The Five Tenets, which set the ground rules for the Brotherhood, but those Tenets have long since been abandoned.
The Dark Brotherhood has been operating in Tamriel for many centuries, at one time having many clandestine sanctuaries across the Empire. They revere Sithis, the avatar of entropy and chaos, as well as the Night Mother, who is the spiritual leader of the Dark Brotherhood.

History

The Dark Brotherhood has been struggling for survival ever since the end of the Third Era. Due to the events of The Elder Scrolls IV: Oblivion, the Dark Brotherhood in Cyrodiil was crippled. They managed to survive until the Great War, when, one after one, each Brotherhood Sanctuary was destroyed. By the end of the War, the Brotherhood was near total destruction once again. Cicero, one of two remaining Dark Brotherhood assassins outside of Skyrim  (the other believed to be a deserter), took the Night Mother's tomb from Bravil to last remaining Dark Brotherhood Sanctuary. In The Elder Scrolls V: Skyrim, the Dark Brotherhood has no listener to hear the Night Mother and thus hears about The Black Sacrament through rumors. This type of life for the Brotherhood continues until the Dragonborn joins them.

Dark Brotherhood Requirements


DarkBrotherhoodAssassination

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"Sweet mother, sweet mother, send your child unto me, for the sins of the unworthy must be baptised in blood and fear."
―The Black Sacrament ritual[src]
Any man or woman may join the Dark Brotherhood. Initiates must display the ability to kill mercilessly, without regret or sorrow. As a result, their ranks include vampireswerewolvesbandits, and mages.
A high sneak skill is recommended before joining the Dark Brotherhood. Jobs done for them often require stealth, to kill an enemy without being detected. A very useful perk for this is Assassin's Blade. To get this, the Dragonborn must have a level 50 sneak skill (along with the other perks leading up to it). It will allow successful sneak attacks with daggers to do 15 x damage.

Attracting the Dark Brotherhood's Attention

The Dragonborn can go to any inn and ask for the latest gossip from the innkeeper. The innkeeper may tell the Dragonborn that Aventus Aretino is trying to perform the Black Sacrament in Windhelm.
Alternatively, if in Riften, the Dragonborn can speak to a man named Maul. He can usually be found standing against a post off to the left at the entrance of the city, if Maven Black-Briar is Jarl, he will be in Mistveil Keep as her housecarl. After sharing some tough words, he can give information on the Dark Brotherhood; for a price, of course. (with a successful intimidation or persuasion, or upon being shown an unusual gem, Maul's information is free).
The children in the Honorhall Orphanage in Riften will also speak about Aventus' attempts to summon the Dark Brotherhood, which will give the Dragonborn a miscellaneous objective as well.  Upon speaking to the children there, they will tell the Dragonborn that Aventus Aretino escaped and has plans to kill their Headmistress, Grelod the Kind, by summoning the Dark Brotherhood.
Speaking with Aventus Aretino in his parent's home in Windhelm initiates the quest Innocence Lost and starts the Dark Brotherhood questline. After accepting Aretino's proposal, the Dragonborn is directed to visit the Honorhall Orphanage. Kill Grelod (the children will cheer and celebrate once she's dead). No bounty is issued for her death.

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The Five Tenets are no longer followed by the Brotherhood.

Joining or Destroying the Brotherhood

24 hours after Innocence Lost has been completed, a courier will appear to the Dragonborn in any city, with a note saying, "We know." A black hand-print is below the words. After receiving the note, sleeping in any bed will begin the next phase of the quest (the acquisition of this note is optional). After some restful slumber, the Dragonborn is seemingly abducted by a Dark Brotherhood Assassin in their sleep and wakes up in an Abandoned Shack. This is where the decision to join or destroy the Dark Brotherhood must be made.
There, the Dragonborn is asked by Astrid, the Dark Brotherhood assassin, to kill one of three people in the room, initiating the quest With Friends Like These. Killing one, two, or even all of the potential victims will earn the Dragonborn an invitation to join the Dark Brotherhood. The Dragonborn may also take the opportunity to destroy the organization by attacking the Dark Brotherhood representative, Astrid. This will initiate the quest Destroy the Dark Brotherhood! (This is the only chance to destroy the Dark Brotherhood, because after joining, the Brotherhood members are otherwise unable to be killed.)

Dark Brotherhood quests