Marty Sklar is one of the last remaining employees who once worked closely with the company's co-founder, Walt Disney.
The 72-year-old said he would leave his executive job at Walt Disney Imagineering to serve as its "ambassador," according to a memo to colleagues Thursday.
He helped to design such park attractions as "The Enchanted Tiki Room," "It's a Small World" and "Space Mountain."
"He understands the Disney way because he learned it at Walt's knee," said Jim Cora, a former chairman of Disneyland International. "He is the keeper of the keys, the conscience, the Jiminy Cricket for the organization."
Sklar said he had long planned to step down after reaching two milestones the 50th anniversary of Disneyland and his own half-century at the company. Last year he reached the first mark, and this June he will hit the other.
The move follows Disney's recent announcement that after its planned acquisition of Pixar Animation Studios this summer, Pixar's creative chief, John Lasseter, will help design rides for Disney's theme parks. Lasseter also will become chief creative officer of both animation studios.
The timing of Sklar's decision was unrelated to Lasseter's pending arrival, Disney officials said.
Low-key and unimposing, Sklar is revered by a generation of designers he trained, dubbed "Imagineers," for his mentoring and his links to the company's heritage. Sklar condensed Walt Disney's ideas into a widely circulated creed called "Mickey's Ten Commandments."