Sir Terry Leahy

In the six years this list has been published, only one man has ever occupied the top spot. Yet by this time next year, Sir Terry Leahy will have retired as chief executive of Tesco following last week’s surprise announcement and that means this will almost certainly be his last time as retail’s number one.

Yet for this year he remains the most powerful man in an industry he has had a profound effect on. Over his 14 years as chief executive of Tesco he has transformed the business, taking it to be the clear number one in the UK grocery market and developing formidable offers in non-food, online, convenience, services and internationally.

A clue to the secret of Leahy’s success came in April, when Asda stated its intention to become the UK’s top non-food retailer. Leahy’s response was withering. “It is better not to predict market share. It is better to look after customers. Customers will decide who is number one,” he said.

It is the mantra that has been at the heart of everything Leahy has done during his three decades with Tesco. And over the past year Leahy’s Tesco flexed its muscles and showed just how powerful its customer understanding and insight makes it. After a difficult first half of 2009 when all three of Tesco’s big four rivals were gaining market share, observers were wondering if it was losing its touch.

The retailer turned to the most powerful weapon in its armoury - one that Leahy himself developed as marketing director - the Clubcard, to lock in its shoppers. The double Clubcard points scheme has been a key driver in helping Tesco to claw back market share from its rivals, particularly Asda.

Not everything over the past year has been plain sailing and Leahy will be disappointed that he is leaving before Tesco’s Fresh & Easy venture in the US has really proved its worth. But Leahy insists its problems are more about the economy on the West Coast than anything to do with the concept.

But overall even his biggest rivals wouldn’t argue with Leahy’s record and he is not just the most successful retailer of his generation, but one of the most accomplished businessmen of this era too.

Leahy’s understated manner has influenced the whole culture of the business. There are no airs and graces about Leahy’s Tesco - it is a down-to-earth, humble organisation that is number one by miles

but thinks with the mindset of a hungry, driven number two.

His successor Phil Clarke (16) is straight from the Leahy mould, even down to coming from Liverpool, and has a strong record as a retailer himself. But he has huge shoes to fill. Retailers of Leahy’s calibre don’t come along very often.