By JAKE COYLE
AP Film Writer
NEW YORK (AP) — Alan Horn, the film executive who helped turn Walt Disney Studios into the most powerful movie studios in Hollywood and whose 50-year career has touched films from from “When Harry Met Sally…” to “The Dark Knight,” is retiring. Disney announced Monday that Horn, 78, chief creative officer of Disney Studios Content, will step down at the end of the year after a nine-year run that coincided with one of the most lucrative stretches of any movie studio. Horn, who was previously co-chairman, oversaw blockbusters that amassed billions in box office from the studio’s divisions, including Lucasfilm, Marvel Studios, Pixar, Disney animation and, after Disney’s acquisition of Fox, 20th Century Studios.