The Brotherhood of Mutants is a group dedicated to the cause of mutant superiority over humans. Throughout its various incarnations, the Brotherhood's agenda has gravitated towards either subjugating the human race to the will of mutants or eradicating humanity altogether.
Magneto formed the Brotherhood of Evil Mutants shortly after the public debut of the X-Men. It's lengthy roster has icluded such mutants as Astra, Toad, Quicksilver, Scarlet Witch, The Blob, Unus, Mystique, Pyro, Avalanche, Destiny, Rogue, Sabretooth, Mammomax, Nocturne, and Mastermind.
The Brotherhood holds a more radical view of mutant-human relations than the X-Men. It has been put forth that if Professor Xavier and Magneto were to be compared to civil rights leaders of the 1960's Xavier and his "dream" would be analogous to Dr. Martin Luther King Jr., wheras Magneto and his stance on Mutant Rights would be more comparable to Malcolm X.