Commander Stern used to tell a lot of jokes, most of which were terrible, but which he thought were very funny. We'd pretend to laugh to make him feel better

I remember my first encounter with Commander Harry Stern. I was about eight and my mother had misread the school term calendar. She thought I was going back on a Wednesday when I was supposed to be back on a Tuesday. So I was a day late for school. I had to walk into the maths lesson and he was the new teacher. I could have been made to feel quite awkward in that situation, but he happened to be very welcoming.

He was a naval submarine commander during the Second World War and immediately after. He got a military decoration for something, but if you ever asked him what for, he'd never tell you. I liked to think he did some work in the secret services, but he'd never talk about it. It was exciting to think you were being taught by a spy, even if there was no truth to it.

He came to St Anselm's prep in 1974 and taught me maths until 1978.

He was old, bald and, even at that stage, quite deaf. His hearing problems were undoubtedly a consequence of his military career. He was about 50; we used to tease him about his age. His mannerisms were slightly military. He had a huge national pride and a great sense of identity around his contribution to his country.

Maths wasn't always an easy subject for me, but he enabled me to become very good at it because of the way he taught it; the enthusiasm and the simplicity of his explanations.

Everything was made simple and straightforward. His style of teaching was to make things interesting and at the same time amusing. He used to tell a lot of jokes, most of which were terrible, but which he thought were very funny. We'd pretend to laugh to make him feel better. But if you didn't laugh, it was never a problem because he'd always laugh enthusiastically at his own jokes. I have never met anyone with such a fantastic capacity to enjoy his own jokes. It was almost as though even he didn't know what the punchline would be.

Because of his deafness, you could have so much fun with him during the lesson. As soon as his back was turned, backchat and chaos would commence, but he would have no idea what was going on. I don't know if everyone else understood him, but I was obviously on his wavelength. Even given the significant age difference, we seemed to have many shared interests; sports, business and horse-riding being three I can remember. I don't think I had preferential treatment, but I would certainly say I had a special relationship with him.

I used to have quite a lot of contact with him outside the classroom. He used to organise the school riding and I'd go riding with him a lot. He would always tell the school that either you had got lost or that the ride had taken longer than expected, so that you'd miss tea. But what he'd actually do was take you back to his house and give you tea. This meant that if you went riding once or twice a week, at least you'd have a chance of getting a decent meal. His wife used to make fantastic cakes. He'd look after those of us who went riding and who worked hard in his maths class.

I told Commander Stern once that I would like to be a millionaire before I was 21. His reply was that I was slightly ambitious, but he was always encouraging. I think I missed my target by a few years. He was part of a foundation that enabled me to achieve it. I'm still in contact with him and my mother sees him often. His wife very sadly died and I was the best man at his second wedding about five or six years ago.

He's about 84 now, but he's still teaching on a private basis up in King's Lynn, Norfolk. There are people who teach and people who are educators, and he's a natural educator; that's his role and his passion. I think if you're an educator you can't just give it up.

Businessman David Ross was talking to Sheryl Simms

The story so far

1965 Born Grimsby

1973-78 St Anselm's preparatory school, Bakewell, Derbyshire

1978-83 Uppingham School, Rutland

1984-87 University of Nottingham

1988 Trainee accountant with Arthur Andersen

1989 Co-founds mobile phone retailer Carphone Warehouse. Company now has 1,200 stores in 11 countries

2000 Carphone floated on stock market

2001 Joins boards of Wembley National Stadium Limited and National Express

2004 Becomes non-executive director of Trinity Mirror

2005 Appointed chairman of Pizza Express. Listed 143rd onSunday Times rich list, worth pound;360 million

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