The Brotherhood of Shadow is an unholy demonic cult from the Mortal Kombat franchise. Founded by the necromancer Quan Chi, the Brotherhood dedicates itself to the worship of the fallen Elder God, Shinnok. Its countless members are ever scheming and planning for his release from the Netherrealm. Its trademarks are stealth, secrecy and deception, and is involved with black magic and necromancy. They achieved their goal when Quan Chi was able to get hold of the sacred amulet needed to free Shinnok from his eternal prison, from where he already controlled the entire Netherrealm. Agents such as Noob Saibot and Reiko rose to prominence during the subsequent war with Princess Kitana, the people of Edenia, Raiden and his Earthrealm warriors during the events of Mortal Kombat 4.
Their joint effort ultimately failed, however, and Shinnok was defeated. In the events leading up to Mortal Kombat: Deadly Alliance and Deception, Noob Saibot began eluding Quan Chi's control and prepared for the creation of his own armies, while Sareena and Ashrah left the Brotherhood. With Shinnok eliminated as a presence to be reckoned with and Quan Chi's own plans with the Deadly Alliance, the Brotherhood seemed to have lost its importance, or at least be on hold. It appears that for most (former) members, their time spent with the Brotherhood was merely a catalyst for more important things to come. It was later revealed in Mortal Kombat: Armageddon that Sareena is working again with the Brotherhood of Shadow, albeit under a spell from Quan Chi. This story is also revealed through her released bio from such game.
At the heart of the Brotherhood of Shadow's fanatical religion is these diabolical zealots' very desire to bring about the day when the malevolent Elder God Shinnok is finally and completely set free from the dark depths of the Netherrealm, and his will is done. They'll stop at nothing to achieve their insidious, Utopian dream of being at the right hand of their divine master and creator, and thus forever rule all creation itself.