Despite never appearing as Darth Vader onscreen, James Earl Jones will be forever remembered for the role—and he deserves the bulk of the credit for bringing the character to life. (Would Vader have been half as memorable without that voice?) But back in the day, Jones was the last to admit that his Darth Vader voice work was kind of a big deal. The actor declined to be credited on A New Hope or The Empire Strikes Back, explaining his thinking to PopMatters in 2008 (via io9).
Jones explained his reasoning, saying, "When Linda Blair did the girl in The Exorcist, they hired Mercedes McCambridge to do the voice of the devil coming out of her. And there was controversy as to whether Mercedes should get credit. I was one who thought no, she was just special effects."
"So when it came to Darth Vader," he continued, "I said, no I'm just special effects." He relented by the time Return of the Jedi rolled around, and his name finally hit the credits.