Fictitious plaintiff
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
A. person appearing in the writ or reconi as the plaintiff in a suit, but who in reality does not exist, or who is ignorant of the suit and of the use of his name in it. It is a contempt of court to sue in the name of a fictitious party.
See 4 Bl. Comm. 134.