

The Brotherhood of Steel are a faction that have appeared in every Fallout game, and are essentially technocratic marines that horde all pre-war technology that they can get their hands on, not trusting anyone else with such equipment. All other faction storylines ultimately resolve in a fight with the Institute. They are the "villain" faction of Fallout 4 because of the nature of their experiments and their lack of concern for those that they effect.

They originated from survivors of the war that holed up at the Fallout equivalent of MIT.

They're focused on studying ways to revive or replicate nature, but in the process are conducting inhumane experiments. Click to shrink.The Institute is a cloister of scientists that live in an underground facility, away from the chaos of the wasteland.
