by Sir David Attenborough

I have never known a man more determined than Adrian. The first time I met him he was sitting in a tiny shoe-box of an office in BBC London doing a very routine job in I think Schools Television. He had asked if we might meet. 'How do I get into the Natural history Unit,' he asked. I told him what I could and said it would not be easy. He looked me straight in the eye. 'I will get there,' he said. There was something about the way he spoke those words - coolly and quietly - that was unforgettable.

I didn't see him again for several years. I had gone to Borneo to make a film about life in the forest canopy. I was told that a new member of the Unit had organised it. It was of course Adrian.

I looked apprehensively at the huge branch a hundred feet up above that I was supposed to get onto - and expressed my doubts.

Once again, that look. 'I will get you there,' he said. And of course he did.

He took me chasing tornadoes across Oklahoma. He even took us all into the stratosphere, tumbling about, weightless, in one of NASA's experimental aeroplanes. As we staggered away from the trip, somewhat queasy and glad to be back on the ground - he - and he alone as far as I can recall - persuaded the pilot to let him go on a second trip the following day - so that he could enjoy it himself.

Needless to say, he chafed in the BBC with its fussiness and bureaucracy. He would have chafed anywhere, I guess, if he did not make the rules. He was a maverick. The most determined of mavericks. And mavericks like him are invaluable and precious and life-enhancing.

The world is poorer now that he has left it.