The original leader of the team was Magneto, a mutant with the ability to control magnetic fields. The other members of the original team were Quicksilver, who can run at incredible speeds, the Scarlet Witch, who has the power to affect probability fields, the Toad, a sinvelling villain with incredible jumping ability and a Medieval costume, and Mastermind, with the power to create illusions of sight, smell, taste, touch and sound. Quicksilver and the Scarlet Witch are twins, and also Magneto's children, although at the time of the original Brotherhood all three of the were unaware of it. Time and again, the Brotherhood clashed with the original X-Men team (consisting of Cyclops, the Angel, the Beast, Iceman and Marvel Girl), until Magneto was captured by an extraterrestrial being called the Stranger. Quicksilver and the Scarlet Witch left the team and joined the Avengers, and the other members dispersed. Later, back on Earth, Magneto reorganized the team three times, including such mutants as the Blob and Unus the Untouchable. Also, the mutant terrorist Mystique organized her own Brotherhood, which she recently reactivated under the name Freedom Force. Members included Pyro, the Blob, Avalanche and Destiny. The Toad also organized a Brotherhood at one point, including the Blob and Pyro, a woman named Phantazia, who could disrupt machines and superpowers, and even Sauron, a pterodacytl of sorts.
In the X-Men movie, the Brotherhood includes Magneto, Mystique, Toad, and Sabretooth.
The Brotherhood is not always so necessarily evil as they are opposed to Professor Charles Xavier's dream of peace with humans. Many of them have been attacked or otherwise harmed, exiled oe espcially hated by humans, which makes them resentful and misguided. At times, many of the Brotherhood mutants have shown signs of reluctance towards harming humans, to the point of Quicksilver even joining the X-Men for a short time. Even Magneto is not entirely evil - in an alternate timeline, he pledged himself to realizing the dream of his friend, Professor X, who had been killed, and was the leader of the X-Men...