Brimstone was once an artificial super-soldier meant to defend an alien race. But he wanted his own freedom in place of his intended purpose. His creators banished him to Earth because of how dangerous he became. 
In his purest form, he becomes a mass of unstable electricity, and can project himself through any screen, as well as creating and controlling fire. He has dedicated himself to finding the scum of the world... and making them pay for their crimes.