Brotherhood of Kain

The Brotherhood of Kain is one of the oldest known mercenary groups. Originating as some form of cult or terrorist organization and always led by a man that takes on the moniker of Kain, the earliest records of the Brotherhood date back to the late 19th century and early 20th century. They were involved in many of the terrorist attacks in the late 20th century and early 21st century, including a large series of terrorist acts in the 2030s. Their most infamous incident though (and almost their last) was the assassination of President Matthew Golson just prior to World War Three; this almost led to their extinction by General Anthony Goodhue.
By the 23rd century, it is known that they were no longer as powerful as before, but why is uncertain. However, they were strong enough to have had major roles in the Interplanetary War earlier and later in the Insurrection. They used a number of illegal weapons, mostly revolving around poison gases and other toxins.
By the 27th century, they are merely a fraction of what they once were, but they are still some of the most deadly saboteurs, assassins and bodyguards in the galaxy.