The Inner Circle appears to have been founded following Kane's apparent death during the Second Tiberium War. At the time, the group was composed of five members: Anton Slavik, General Marzaq, and three other unnamed members.
As the Inner Circle members bickered among themselves, each vying for power, Slavik sought to unite them to prepare for Kane's arrival. To that end, he ordered one of his commanders to assasinate many of his rivals. However, Marzaq continued to lead the opposition to him. In order to help reunite the shattered Brotherhood, Slavik ordered the Commander to recover CABAL's core from GDI.
However, CABAL bypassed Slavik and issued a series of unauthorized orders to the Commander, leading to the assassination of Tratos and the recovery of the Tacitus. The Inner Circle members demanded Slavik to shut down CABAL. In resposne, CABAL assassinated them using its cyborgs, leaving Anton Slavik the sole surviving member of the Inner Circle.
Third Tiberium War
Following the Firestorm Conflict and the return of Kane, the Inner Circle was reestablished and regained its role as advisors to Kane and his most loyal followers. The Inner Circle during the Third Tiberium War included Brother Eamonn, the aforementioned Nod commander, an unnnamed advisor, and Kilian Qatar before she was framed by Abbess Alexa Kovacs. After the conclusion of the Third Tiberium War, Kane's most trusted commander became a member of the Inner Circle.