Heroes find him as an ally at the end of the Mender Silos Task Force.
Villains face him in the following missions:
- Steal synthetics from Citadel from Dr._Forrester (Levels 40-44)
- Kidnap Dr. Murphy from Ghost Widow (Levels 45-50)
- Destroy Statesman and Freedom Phalanx from Lord Recluse (Levels 45-50)
- The final mission of the Mender Silos Task Force.
Originally named Bastion, Citadel was the very first android hero. In the initial Rikti onslaught, he took heavy damage, and was almost completely destroyed. With Positron's help, scientists at DATA created a second version of Citadel using the old model's original memory core and the remnants of a power suit, once worn by the hero Horatio. He now works on Talos Island issuing Task Force missions and consulting DATA on development of all AI-based robots. Citadel does not fully understand human ways, but he is a valiant defender of Paragon City.
Citadel was named Bastion before DATA gave him a substantial upgrade to his systems enhancing his capabilities. In honor of his new abilities, he renamed himself "Citadel".
Citadel's sidekick is Luminary although she has become a full-fledged hero in her own right as a member of the Vindicators. Luminary has more advanced systems but doesn't have the experience of Citadel so he keeps a watchful eye over her.
- Previously, Citadel was named Bastion. The name was changed because of Marvel's complaint that the devs had gotten the name from their Bastion, who was introduced in 1996.
- Citadel's Praetorian Earth counterpart is Siege.
- Citadel first appeared in Top Cow's City of Heroes #4.