Star Wars was one of the first films to spiral into a phenomenon, offering fans clothing, figurines, cereal, stationary, and other oddities, and also beautiful publications of pre-production artwork from McQuarrie.
George Lucas has commented:
"Ralph McQuarrie was the first person I hired to help me envision 'Star Wars,'" Lucas said in a statement. "His genial contribution, in the form of unequaled production paintings, propelled and inspired all of the cast and crew of the original 'Star Wars' trilogy. "When words could not convey my ideas, I could always point to one of Ralph's fabulous illustrations and say, 'Do it like this.'" - Source
Whilst George Lucas imagined the characters, the plot, the setting and the players in the story, Ralph McQuarrie visualized it. Spend a moment looking at his outstanding pieces and you'll appreciate how far his legacy has reached.