- Pangborn: "We've endured worse."
- Magnus Bane: "You've inflicted worse."
- ―Magnus encountering Circle members, The Mortal Cup
The Circle was formed by Valentine, and some of his followers believed that their goal was the protection of humans, like all Shadowhunters. However, Valentine was willing to go to great lengths and sacrifice lives to achieve his goals. At one point, they led a revolt that got a lot of Shadowhunters killed. Valentine intended to use the Mortal Cup, to create new Shadowhunters and control demons, and could have destroyed the Shadow World and humanity had his wife Jocelyn not stolen it from him.
Some of its members repented, and the Circle runes on their necks were charmed so that they would never speak of the Circle again. The Shadowhunters have since been forbidden to even hear about the Circle.
Valentine kept a part of his group active. Many of his followers remained loyal to him and worked with him. For a time, they operated out of a base in Chernobyl. When he got ahold of the Cup, he was able to recruit more members—both Shadowhunters and mundanes he was able to turn alike—to join him and the Circle, with a ship as their primary stronghold until it was compromised. No activities from the group has been noted since Valentine's death.