I had never been on a stakeout, but I knew how it was done. I took a book. I bought a few sandwiches. I flipped on the radio and listened to the traffic reports. That kept me awake as I waited for my target: Grigori Yakovlevich Perelman .

I was here to interview him, but I had a problem: Perelman was a recluse – possibly the most famous recluse in the world – and hated talking to people.

Regarded by many as both the cleverest and the craziest person on the planet, the 46-year-old first came to the world’s attention six years ago when it was announced that he’d solved an unsolvable maths problem.