When Frank Blake, chief executive of Home Depot, the world's largest home improvement retailer, wants to pay an unannounced visit to one of the company's 1,900 US stores, he sometimes wears a hat to disguise his large and noticeably unhairy head.

Most of the time being bald is “an advantage”, he says, but not when snooping around the shop floor. “When people see me, they go: ‘OK, I've got it: it's the bald guy',” he says. “But if I wear a hat, that actually makes it a little more difficult.”

Few employees would have recognised Mr Blake, even without a hat, when he arrived in the top office at Home Depot in January 2007. He took over from Bob Nardelli, the high-profile chief executive who resigned after a shareholder revolt over the retailer's declining performance.