Somebody's alternate personality or persona; another self.
A very close and intimate friend.
A corporation used by a person to conduct personal business in an attempt to shield himself or herself from personal liability, and which a court may penetrate by "piercing the corporate veil" to impose liability on the person when they commit fraud or injustice.
A friend, associate or colleague.
Research into one's opponent's family, friends, and past, which aims to uncover activities or interests which embarrass or discredit them.