Alphonse Elric and his brother attempted some transmutation, which caused Alphonse to become trapped in a suit of armor. During the course of the series he tries to stop some villains from taking over the world, but also tries to get his old body back, so that he can do normal things like eat and sleep again.
Alphonse is somewhere around eleven years old during the course of the series and he does not age at all because his body is a suit of armor, so he is very youthful. Like most youths he is naive, endearing and uninhibited. He has a strong sense of morality and always tries to do what is right even at the cost of his own body. He also sticks with his brother through all kinds of hell. He is a great guy to have on your side because not only is he loyal, his large suit of armor makes him very powerful physically. He can protect people with his body from weaker attacks such as bullets and wield a devastating punch.