George Lucas really screwed him. First he didn't even know he wasn't the voice of Vader until the premiere of the movie. Second his contract for "Return of the Jedi" was a percentage of the profit. The studio claims the movie did not make a profit. It grossed $475 million on a budget of $32 million.
Of the actors listed in Star Wars's credits, I think only eight are still with us.
Mark Hamill (Luke)
Harrison Ford (Han)
Anthony Daniels (3PO)
Dennis Lawson (Wedge)
Garrick Hagon (Biggs)
Jack Klaff (Red Four)
Anges MacInnes (Gold Leader)
Leslie Schofield (Commander)