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who plays darth vader in the return of the jedi
Although David Prowse played the costumed scenes and James Earl Jones voiced Darth Vader, Sebastian Shaw was cast in a single scene.
what was the scene in which Sebastian Shaw played Darth Vader
Sebastian Shaw was cast in a single scene aboard the second Death Star when Luke Skywalker unmasks his dying father.

Question: why was he picked for the role
Self-contained rewrite: why was Sebastian Shaw picked for the role of Darth Vader in Return of the Jedi