The Dark Brotherhood is a guild of assassins shrouded in shadow and mystery which has been active all over Tamriel. While their business is certainly not legal, their existence has typically been tolerated or ignored. Whenever an individual with legal authority takes an interest in their dealings, the Brotherhood relies upon a combination of bribery, blackmail, coercion, and murder to keep their activities hidden. They have been bitter rivals of the Morag Tong since the Second Era. The Brotherhood is also known for their worship of the Dread Father Sithis. Dark Sisters are accepted into the Brotherhood as equally as Dark Brothers, though members of either gender are often referred to as Brothers.
Like any organization, the Dark Brotherhood has some rules that all members must abide by, though the demand to adhere to them can vary with the leadership. These interrelated rules are the Five Tenets: members must never dishonor the Night Mother, betray the Dark Brotherhood, disobey or refuse to carry out an order from a superior, steal the possessions of a Dark Brother or Dark Sister, or kill a Dark Brother or Dark Sister. Breaking one of these tenets invokes the Wrath of Sithis, which, it is rumored, is not just a turn of phrase.
The leader of the Dark Brotherhood is the mysterious, elusive Night Mother. Some stories suggest that the current Night Mother is the ghost of the first, who became the wife of Sithis and murdered their five children in his honor. Others say that the title is merely an honorific given to the current leader. Some even consider her to be none other than Mephala. Regardless, the most well-known and infamous method of acquiring the services of the Brotherhood is by performing the Black Sacrament, a profane ritual that purportedly allows those who perform it to be heard directly by the Night Mother. The ritual involves stabbing some actual body parts (including a heart, skull, bones and flesh) within a circle of candles using a dagger rubbed with the petals of a Nightshade plant while whispering the plea, “Sweet Mother, sweet Mother, send your child unto me, for the sins of the unworthy must be baptized in blood and fear”. Next in the command hierarchy is the mysterious Black Hand, which is composed of a Listener and four Speakers. The Listener, of course, listens to the Night Mother, and relays her orders to the Speakers, who then dispatch a Brother to make specific arrangements and carry out the murder. Their identities are kept well-hidden, even within the organization.
The Brotherhood’s origins are connected with the Morag Tong, though how is a topic still debated by scholars. One popular theory holds that the Brotherhood split away for religious reasons. In the year 1E 2920, the Morag Tong assassinated Emperor Reman III. The Tong later performed an equally high-profile assassination in 2E 324 of Reman’s successor, Versidue-Shaie, who had ordered Reman III assassination over 300 years before. This started a frenzy among the nobles across Tamriel, and the Morag Tong was outlawed across the continent. The Morag Tong appealed to the highest power in Morrowind to ensure their existence. The highest power in Morrowind at that time was the Tribunal.Mephala, whom the Tong worshipped as their patron goddess, was seen by the Dunmer as the Anticipation of the Tribune Vivec. The suspicion is that in exchange for tolerance of their continued existence, the Tong ceased their worship of Mephala in exchange for the worship of Vivec. This is where the break would’ve occurred – the Morag Tong agreed and worshipped Vivec, whereas the Dark Brotherhood apparently objected and broke off. A similar but distinct theory is that, following Versidue-Shaie’s assassination and the subsequent persecution of the Morag Tong, Sithis spoke to a former member and demanded the formation of a new guild of assassins to “marry business with death” and better satisfy the Void‘s hunger for souls, a guild which would worship him and not Mephala.
Another story, taken from a purported interview between author Enric Milnes and the Night Mother, says the Dark Brotherhood was an offshoot of the Thieves Guild, not the Morag Tong. Milnes was assassinated shortly after he had it published. This account asserts that, some time in the Second Era, a few members of the Thieves Guild found it efficacious to strangle the occupant of the house when performing a burglary. The woman who would become the Night Mother thought they should formally recognize and allow murder, but the leadership of the Thieves Guild at the time disagreed (and still do), thinking it would be bad for their core business. Undeterred, she founded the murder syndicate which would become the Dark Brotherhood. The connection to the Morag Tong only emerged after the assassination of Potentate Savirien-Chorak in 2E 431, when several Tong assassins quit that struggling organization and joined the upstart syndicate. Who murdered the last Potentate has never been clearly established, though some accredit the Brotherhood with the “accounting” of the Akaviri.
Despite all this conjecture, more is known about the exact date of the formation of the Dark Brotherhood. In 2E 358, a note addressed to “Brother” was found beneath the floorboards of an abandoned house in the Nordic village of Jallenheim which depicted a war going on between two shadowy organizations. Scholars speculate that this note is a rare piece of evidence about the war between the Morag Tong and the Brotherhood. This would make this note the first recorded evidence about the existence of the Dark Brotherhood. About fifty years later, in 2E 412, the Blood Queen Arlimahera of Hegathe wrote a short piece in her journals, mentioning that her family had enlisted the services of the Dark Brotherhood since her grandfather’s time. Together with the note found in Jallenheim, this puts the formation of the Dark Brotherhood around 2E 358 or 360 at the latest.