Alan Horn presided over a studio that was never the flashiest or sexiest in town, but was certainly the steadiest, usually the most prolific and often the top grossing.

On Friday, the 68-year-old Horn spends his last day as president and COO of Warner Bros. He leaves (or, rather, assumes a consultancy) after 12 years atop the company, with a track record that includes two Best Picture winners ("Million Dollar Baby" and "The Departed") along with "The Dark Knight," "Inception," "Ocean's Eleven" and a number of movies from the filmmaker he reluctantly singles out as his favorite, Clint Eastwood.

But of all the films with which Horn has been associated, the ones that have left the strongest mark on Warners' bottom line are the eight movies in the "Harry Potter" series, which began with "Harry Potter and the Sorcerer's Stone" in 2001 and will come to a close this summer as the most successful franchise in motion picture history, topping even the James Bond series with a total gross of $6 billion and counting.

"It took a huge emotional and financial investment from Alan to get the franchise off the ground," "Potter" producer David Barron told TheWrap. "He was always our biggest champion, and it was never about ego with Alan. For such a huge and powerful person in Hollywood, he was ever the gentleman."

Also see slideshow: 'Potter' to 'Dark Knight' to 'Inception': The Legacy of Alan Horn [5]

To salute Horn on his final day in office, the "Potter" franchise's executive producer David Heyman told TheWrap about a decade's worth of experiences with the executive who was not betting on a sure thing when he first optioned a book about a boy wizard:

I think it's safe to say that "Harry Potter" would not be what it is without Alan Horn. Alan is decent, loyal, straightforward and is a Harry Potter fan -- in fact, not just a fan, a maniacal  fan. He gave us the support, the resources and the independence that we needed to make the films we did the way we did. 

When the first Harry Potter book was optioned, it wasn't a big bestseller. People forget about that. I read the book before it was published, and I sent it to my friend Lionel Wigram, who was a vice president at the studio. And I think mostly out of a feeling of "let's give Heyman a shot," they optioned it.

It was not a big option, it was an inexpensive option, and I don’t think anybody read the book for a while. But over time, as Alan read the books and became more involved in them, he was someone I could always go to. You knew was looking out for the books' interest, and the films' interest.

The Harry Potter films were not inexpensive films. Yes, they did well, but it was risky at times. And Alan never wavered. He supported the choices of directors that we made, whether it was Alfonso Cuaron or Mike Newell or David Yates. Mike had had successes, but he was coming off a bomb. Alfonso was a great filmmaker, but he'd just made "Y Tu Mama Tambien." With a big franchise like Harry Potter, to bring in a director whose last film was "Y Tu Mama Tambien," you can imagine what people thought Harry, Ron and Hermione were going to get up to. And those conversations would have been very different at any other studio.

(laughs) I don't want to pretend that Alan said, "Oh, what a great idea, let's do it." No. There was a little bit of stomping and jumping up. But it's easy for me as a producer to say, "Alfonso is the right person, we believe in him, we've got to do it." It's not so easy for the money to say that. And Alan did.

When he read the scripts Alan would give notes, and when he saw the films he would give notes. And his attention to detail was remarkable. The notes we got from Alan were always really specific, and inevitably related to the book.

(Pictured: Horn with Daniel Radcliffe, Emma Watson, Rupert Grint, Tom Felton and  Heyman)

He was a huge fan of the books, so certainly there were discussions with him about the changes we made and the things we left out. But ultimately he understood that choices had to be made, and he also understood that the films were different from the books, as did Jo [author J.K.] Rowling. If Jo was happy, then Alan was happy. And that was the card that I could always play.

The support that the Alan has given Jo's work is remarkable. When we first sold the books, she had no control whatsoever, no final say, nothing. But Alan respected Jo, and he respected the work. Because of Alan Horn, we were able to protect the books. He encouraged that protection in ways that you can't even begin to imagine.

If you look at the Warners production executives, the physical production team, the marketing team, we had amazing support. That all stems from the man at the top. And I think that philosophy is something that is going to be carried through in his succession. I think that Jeff Robinov is going to do that. That's one of the things that's exciting about Warners as a studio – they really back, build and believe in filmmakers.

Personally, I owe Alan Horn so  much. He's really, really decent man, and I think he'll be greatly missed in the film community