His name did not originally appear in the ending credits of
Star Wars (1977), though he was credited in
The Star Wars Holiday Special (1978). At the time of the film's release, he felt he hadn't done enough to deserve a credit. His name was added to the special edition release of the film in 1997.
Lucas liked his commanding voice very much and had no intention of using
David Prowse's, who spoke Vader's lines during filming.