Thomas Staggs, considered the likely successor to Chief Executive Robert Iger at the Walt Disney Co., is stepping down as Chief Operating Officer, it was announced Monday. No explanation was given for his departure. Staggs will leave the Burbank entertainment and media company effective May 6 but remain as a special advisor to Iger through the end of the fiscal year on Sept. 30. Staggs was named chief operating officer in February of last year, a move seen as making him the successor to Iger when he steps down as chief executive in 2018. Staggs had previously been Disney’s chief financial officer and headed up the theme parks and resorts division. Iger called Staggs a great friend and trusted colleague for more than 20 years. “He’s made important contributions to this company, earning wide respect across the organization for his achievements and personal integrity,” Iger said in a prepared statement. “I’m proud of what we’ve accomplished together, immensely grateful for the privilege of working with him, and confident that he will be enormously successful in whatever opportunity he chooses.” Staggs said he was grateful for the opportunity to work for Disney and with Iger during a period of unprecedented growth and transformation. “Disney truly stands alone, not only because of the company’s phenomenal creativity, but also because of the thousands of remarkable people who make it such an extraordinary place,” Staggs said in a prepared statement. The next step by Disney’s directors is to identify and evaluate more candidates as eventual replacements for Iger. The news on Staggs broke after the market closed. Shares closed down 39 cents, or a fraction of a percent, to $98.68 on the New York Stock Exchange. Shares were down almost 2 percent in after-hours trading.