Through various universes, multiple versions of a scientist named Rick Sanchez have been involved in resistance groups against the Galactic Federation, as well as other groups who consider their genius a threat, such as galactic terrorists, sub-galactic dictators and most of the entire Intergalactic government. To protect themselves and hide from opposing groups, a "few thousand" alternate versions of Rick decided to join together and create their own society. It is presumed the Citadel was in a dimension specifically created by Ricks. The Citadel is known to have existed for at least 15 years. At the time of its foundation it was likely solely inhabited by Ricks, who would have been in their 50s or younger, but more and more Ricks continue to join the Citadel to this day.
A force referred to as the "Citadel's militia" performs military and security duties for the Council of Ricks. The militia is comprises mostly of uniformed Ricks, including their commander-in-chief, but some Mortys are also in their ranks.