I'm not sure where to start when looking at Philip's legacy as it is overwhelming in its scope and depth. But that immediately tells you a lot about his choices. He was the best character actor I can think of, and if you look at just the smaller roles he occupied, then those performances alone set him apart from his contemporaries. His strength was a total immersion in the role and a lack of vanity. At the same time, he hated what he loved, that was his curse – he would tear himself to pieces over his performances.

It was my girlfriend Nimi who, upon reading the script of A Most Wanted Man, immediately suggested I approach Philip Seymour Hoffman; in retrospect, there was only one choice. It was obvious that he would be the person to bring this John le Carré character to life. I always imagined this man to have a strong physicality as well as intelligence and a certain kind of leadership. When Phil and I watched the film together in its early stages, I could not believe that the guy sitting next to me was the same person as the one on screen. The belief in the reality of his character was total. Despite any issues he was dealing with outside of the film, domestic or otherwise, the performance never suffered.

Our first meeting was on a still shoot I did with him for Vogue in New York in 2011. While they were mending his trousers in an adjacent hotel room, we used the downtime to discuss the film and his role. He was sitting in his underwear, of course, but he never let his focus shift to the absurdity of the situation. He was serious about the work.

Initially there was some unease between us on the set of A Most Wanted Man, which I attribute to my inexperience as a director and in not verbalising my needs from actors in a way they are used to. But, gradually, Phil and I got to a place where the movie started to flow naturally and he didn't need much direction any more; he totally became the character of Günther Bachmann. He even signed off as Günther on an email to me when he got back home, after the film finished.

His character had a team of young detectives, Nina Hoss and Daniel Brühl among them, and on and off set he would be very much like their mentor. He would be protective of them and available as an actor with advice or encouragement. On the other hand, he would not hang out with actors who played roles that he, as a character in the film, had no time for. At night, we exchanged emails over scenes to come and to work out where we were going with it. He had a incredible take on his character and the film as a whole and it was fantastic to share this with him. We bonded over many things in the end, music being one of them. I made him a tape of songs I wanted to use in the film which he loved very much, particularly the Tom Waits track Hoist That Rag, as he too had been listening to it recently.

Phil and I had dinner with our partners Mimi and Nimi in the late summer and he was a wonderful spirit and company to be with. He was a giant of a man in every way imaginable and his demise is not only a tremendous loss to the world at large and to lovers of great art, but very much on a human level. He was 200% human, with all the struggles and flaws that come with this – and that is where that great art came from, I like to think.

It is unlikely I can do him justice with my writing but I like to think I did him justice in the film we made, where he is outstanding, and deserving of all our attention. I know he was extremely proud of it and we were talking about working together again when we met two weeks ago. As he put it: "I hope we get to do this again on another film. We know more now and I feel we'd fight well together and be unshakeable, and that's exciting."

Alas, it will never be and that makes the end of our film even harder to watch.

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