The Bane of Christopher Nolan's "Dark Knight" trilogy is one of the most enigmatic comic book villains to be portrayed on the big screen, but apart from working with the League of Shadows, his origin is completely unknown. However, the mask might be the key to unlocking his true backstory.
After Bane defeats Batman and traps him in The Pit, Batman learns Bane was also a prisoner there, where he received poor medical treatment after being beaten by the other inmates. During Bane and Batman's final fight, Batman breaks the mask and incapacitates him, indicating that the mask has something to do with his injuries.
Rolling Stone reported that Christopher Nolan said “the mask dispenses a type of anesthetic that keeps his pain just below the threshold so he can function." This isn't too far off from the function of Bane's mask in the original comics, which dispenses the experimental chemical called Venom directly to his brain.