Any time I try to describe Heath it becomes a series of clichés, because he was extraordinary and, unfortunately, most of those clichés have already been used up on lesser people.

I met him for the first time in LA around 2001, when we were working on The Brothers Grimm. He was a ball of energy, firing on all cylinders, and he had a magnetic quality. I liked him immediately and even though I hadn't actually seen Heath in anything at that point,

I said to him: 'You're on. Let's do it.'

He was one of those blessed human beings who have the facility to do so many things at the same time. When he wasn't acting, he was directing music videos and supporting young musicians. He was working on the script for a film he was preparing to direct. He had an incredibly artistic side, and he was practically a grand master at chess. That's why, when he died, it was as if half of the world had collapsed.

He died halfway through the film I'm currently making, The Imaginarium of Doctor Parnassus. We had finished shooting in London on Saturday night. On Sunday, I went to Vancouver to prepare for the next stage and Heath went to New York. He was supposed to be turning up in Vancouver on the Friday. On Tuesday he was dead.

None of us could deal with it. It was impossible - that was the problem. It was absolutely impossible that this could be a fact. But there it was. I was working in the art department when I heard the news, and we stayed there all afternoon. At sunset, thousands of ravens flew over the window and I thought: those are the ravens from The Brothers Grimm, and they are all going to salute Heath.

In terms of his acting, it still rankles with me that he's dead because he would have been streets ahead of anyone else in his generation. He just kept getting better and better. He was fearless. On Parnassus, he was improvising all the time and it was better than what we had written. I don't normally encourage that kind of improvisation, but in a sense I felt Heath was writing this film. He was an incredibly funny performer when he wanted to be - his comic timing was just extraordinary - and then he could break your heart the next minute.

Usually, with actors, it's all about themselves. But it was never like that with Heath. He was completely supportive of everything else around him. He got better performances out of other actors - he just drew it out of them. He was utterly generous and always aware of everyone else, and he behaved as if there was nothing special about him - he was just a guy.

His physicality was extraordinary, too. I remember Monica Bellucci turning up to make Grimms. She went into the make-up room and Heath's picture was on the wall. She hadn't met him and I don't think she knew exactly who he was, but immediately she went, whoosh, to that picture. That was the kind of attraction Heath had. Women adored him and men loved him.

We've all agreed to call Parnassus 'A film from Heath Ledger and friends' because I don't think it is a Terry Gilliam film. I think it's something that his life and death has created. When he died, I said it was over. We can't carry on. But everybody said, 'You've got to carry on' - for the film, for Heath's last performance. It wasn't possible for any one person to replace him so we made the quantum leap and got three people - Johnny Depp, Colin Farrell and Jude Law. The Holy Trinity. They came in and they pulled it off and I think it works brilliantly.

When he died, there were all these nonsensical stories coming out about Heath Ledger, James Dean and River Phoenix, all destroyed by the system - but that's bullshit. What happened was an absurd accident. I still don't understand it. I know he was exhausted - the last thing he said was that he was so tired and just wanted to sleep. You actually think at certain times angels come down to earth and Heath might have been one of them. And then he's gone and you think: this is all wrong, all the other people should be dead. He should be leading us all into a wonderful world of adventure.