LOS ANGELES — Thomas O. Staggs, the favored contender to lead Disney after Robert A. Iger’s retirement, unexpectedly announced his departure on Monday, throwing succession at the world’s largest entertainment company into disarray.

Mr. Staggs, who became the Walt Disney Company’s No. 2 executive last year, beating out another candidate, will step down as chief operating officer on May 6. Disney said that Mr. Staggs, 55, would remain an employee until the fall, serving as “special adviser” to Mr. Iger, who is the company’s chief executive and chairman. In a statement, Mr. Iger called Mr. Staggs “a great friend and trusted colleague.”

Disney has a history of bumpy transitions of power. And last year, when Mr. Staggs was elevated to chief operating officer from theme park chairman, Disney insisted that it was not a coronation. Disney acknowledged, however, that the promotion made him Mr. Iger’s handpicked heir, pending the board’s approval. Mr. Iger, 65, said in 2014 that he would step down in June 2018, a two-year extension from a previously announced retirement.

After the promotion, as Mr. Staggs came under intense scrutiny by Disney’s board, it became clear that at least some board members were not convinced he had the skills required to maintain Disney’s creative momentum. While Mr. Staggs has extensive financial experience, his résumé is light when it comes to the successful creation of movies and television shows. (For his part, Mr. Iger ran ABC early in his career.)