Robert Iger stepped aside as chief executive of Walt Disney Co., though he will retain significant power over the company that he expanded into Hollywood’s biggest and most powerful entertainment conglomerate over a more than 14-year tenure.

Disney on Tuesday named the company’s head of parks and resorts, Bob Chapek, CEO effective immediately. But Mr. Iger will stay on as executive chairman, overseeing the company’s creative endeavors through the end of next year, when his contract expires.

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