In a statement, Cook says he is resigning as chairman of Walt Disney Studios, effective immediately. He says he has loved "every minute" of his 38 years with the company.
He says he's been contemplating the move for some time and feels that now is the right time to move on.
Cook's studio has come under intense scrutiny for the quality of its films.
In response to Cook's resignation, Disney Chief Executive Bob Iger said, "Cook's outstanding creative instincts and incomparable showmanship have truly enriched this company and significantly impacted Disney's great legacy."