The Sith Council were a massive group of Sith who advised the one true Dark Lord of the Sith.
Major Story Arcs
Old Sith Empire
This Council convened in a great citedal on Ziost. The Sith Council managed the affairs of the Empire. Each Lord that sat on the Council personally ruled over a minimum of a dozen worlds.
After Marka Ragno's death, two Lords on the council, Naga Sadow and Ludo Kressh, fought over the position of Dark Lord of the Sith. This conflict created a rift within the council, with several lords siding with Kressh, and the rest siding with Sadow.
Eventually, Sadow was able to convince the council to make him Dark Lord after he convinced them that the Galactic Republic was executing hit-and-run attacks within the Empire. After Ludo Kressh discovered the deception, he and two other lords attacked Sadow's fortress, but they were soundly defeated, and Sadow secured his hold over his title.
The only council member known to have survived the Great Hyperspace War was Naga Sadow. This tradition of a Sith Council was apparently not continued by Sadow's successors, Exar Kun and Freedom Nadd.
Resurgent Sith Empire
Revan's Sith Empire
Although no information is given, it can be speculated from Revan's comments to Darth Bane in his personal holocron that no Sith Council existed under his rule; Revan believed that the Sith needed to be ruled by a single individual, the epitome and symbol of the power of the Dark Side, in order to stave off destruction by the squabbling of lesser beings.
New Sith Empire
In the New Sith Wars, Keen seemed to have resurrected this council with himself as its ambiguous head. Unlike earlier councils, except for the Dark Council, each member actually held the title Dark Lord of the Sith in his own right; however, unlike the Dark Council, all of Kaan's Council members, including Kaan himself, were at least nominally equal, making for a far murkier chain of succession. However, while only ten Dark Lords were ever seen on the council, at least sixteen others were known to have existed at the time.
Lost Tribe of Sith
On Kesh, the Lost Tribe had established their own version of the Sith Council known as the Circle of Lords. The Circle was located in Kesh's capital city of Tahv. It consisted of a Grand Sith Lord, who served as the head of the Circle, seven High Sith Lords, and thirteen Sith Lords for a total of twenty one members.