The Brotherhood of Mutants is an underground group formed and formerly led by Magneto. It originally stood for the superiority of Homo-Superiors over Homo-Sapiens, and the uprising hope of the downtrodden mutant. However, when Magneto dissolved the group, Mystique picked up the torch for her own personal agendas. The group most commonly comes into conflict with The X-Men but has been known to fight other hero teams such as the Avengers and the New Warriors. Anti-Mutant groups often refer to them as 'The Brotherhood of Evil Mutants'.
Magneto dissolves the Brotherhood of Mutants after a few failed terrorist attacks, discouraged by repeated defeat and the rejection of his family.
Mystique reforms the Brotherhood of Mutants for her own goals, following the advice of her precognative lover Destiny. They perform various acts of terrorism and come into conflict with several hero groups like the X-Men and the New Warriors.