Bryce Shumar was the captain of the Daedalus-class USS Essex, lost over two centuries before Power Play, whose identity is claimed by the entity that takes possession of Deanna Troi.
Bryce Shumar is central to the fifth-season episode Power Play, though the man himself is long dead. He commanded the USS Essex, which vanished in 2167 and was in fact destroyed in the electromagnetic storms of a moon of Mab-Bu VI.
When Troi, Data and Miles O'Brien are possessed on that moon and seize Ten Forward, the presence in Troi announces itself as Shumar and says that the others are his officers, their spirits trapped since the wreck and wanting only to have their remains taken home.
Jean-Luc Picard doubts the story, and rightly: the intruders are condemned prisoners from a penal colony seeking bodies in which to escape. The real Shumar and his crew died with their ship.