The Forever Knights are a massive secret organization that are led by several different people as they all have different goals. 

Ben 10

The Forever Knights first appear in A Small Problem, where they take Grey Matter from Howell Wayneright and plan to dissect him. Howell helps Grey Matter escape, and he then creates a bomb which causes their castle to explode. This made their leader Enoch angry with Ben and he then planned to learn everything about him, Gwen, and Max Tennyson.