The Mandarin Bailiff is the robed court officer who calls Q's recreated post-atomic horror tribunal to order when Picard and his officers are put on trial for the crimes of humanity.
The Mandarin Bailiff appears in Encounter at Farpoint, the opening story of The Next Generation. He is part of the illusion Q builds around Picard, Data, Troi and Tasha Yar: a rowdy courtroom modelled on Earth of 2079, in the lawless years after the Third World War.
Dressed in ornate robes, the Bailiff announces the judge, orders the prisoners to stand and reads out the charge that humanity is a grievously savage race. He takes evident pleasure in the ritual of the court and in the soldiers who enforce it.
Whether he is a real being, a puppet or simply another face of Q is never explained. The courtroom returns in All Good Things, though the Bailiff is chiefly remembered from the first trial.