The Producers Guild has bestowed its Milestone Award on many larger-than-life showbiz characters over the years. Alan Horn is not one of them.Before arriving in Hollywood some 35 years ago, Horn worked at Procter & Gamble, and it shows. Warner Bros.’ prexy-COO takes a very businesslike approach to the film biz, avoiding the theatrics that constantly erupt on other lots for a smoother stewardship. His exec team has been with him for years, not months. Horn was running Castle Rock Entertainment, which produced “Seinfeld” and “When Harry Met Sally” under his watch, when he and chair-CEO Barry Meyer were tapped to fill the shoes of former studio toppers Bob Daly and Terry Semel. Under the Horn-Meyer pairing, Horn has had closer oversight of the film operation and Meyer more say over the studio’s TV biz. However, the pair just initiated a major reorganization of the film operation that will free up Horn to focus more on strategic issues. Horn has developed strong ties in the creative community over the years, nurturing the “Harry Potter” franchise by working closely with scribe J.K. Rowling, and maintaining a close bond with Leonardo DiCaprio through projects and their shared work on behalf of the Natural Resources Defense Council. He’s still tight with Castle Rock crony Rob Reiner, who recently directed “The Bucket List” for the studio. PGA exec director Vance Van Petten says the guild selected Horn for the kudo, which has previously gone to the likes of Louis B. Mayer, Cecil B. DeMille and Bob Hope, to honor his achievements as a producer and studio chief. “It’s an incredible background,” Van Petten says. “And he’s really, really well liked.” Eight years into his run at Warner Bros., it’s still working for Horn: The studio just pulled in a record $2.24 billion at the international B.O.; for the seventh year in a row the studio generated more than $1 billion at the domestic B.O.