Alphonse's soul is bonded to a suit of armor after a botched attempt by him and Edward to revive their mother has costed him his entire body in an "equivalent exchange".
The calmer of the two, Al is tasked with keeping his brother in check. Is often mistaken as the older brother by others (much to Ed's chagrin) and for a robot by those outside the fanbase.
This tag is applicable to both Alphonse's armor form and his actual human form that he has regained at the end of FMA.
