The Chief Bridesmaid
The chief bridesmaid - traditionally called the Maid of Honour (unmarried) or Matron of Honour (married) - is usually a close friend or sister of the bride.
The bride must choose her chief bridesmaid carefully: she must be a confidante and a trustworthy friend.
It is important that she understands the idiosyncrasies of the bride; the groom should also have confidence in the choice of the chief bridesmaid.
She is the bride's main helper. This will include involvement in plans before the wedding and acting as her key aide on the day.