The Business On... Ken Costa, Chairman, Lazard International

Nothing to do with the coffee chain then?

No, but Mr Costa, until now one of the City's most senior rainmakers, will have plenty more time for sipping cappuccinos from this weekend onwards. He announced his departure from Lazard yesterday in a move that shocked the City.

What's the big deal?

Just that no one had been expecting him to go and the reasons for his departure are not at all clear. He joined Lazard in 2007 after a 30-year career at SG Warburg (during the final decade the bank was owned by UBS). He was personally hired by Bruce Wasserstein, one of investment banking's biggest names.

So where is he going now?

No one is saying, though sources close to Mr Costa say he has no intention of retiring. His departure will be considered a blow to Lazard though – and it is still getting over the loss of Naguib Kheraj, another powerful figure in the City, who quit as chief executive of Lazard International earlier this year, after only 32 days at the firm.

Still, aren't these bankers always up to something?

That's a rather unfair suggestion in the case of Mr Costa, who wears his moral compass on his sleeve. He's a committed Christian who has always insisted his religion informed his work. "People often ask how I reconcile being a banker and a Christian," he once said. "The market economy remains a good servant but a bad master, it needs to operate within a wider moral context."

So do we know anything else about him?

Well, he's a South African by birth and was active in the campaign against apartheid during his younger days. Now 62, he's the chairman of Alpha International, the organisation that promotes the Christian faith through its well-known courses. He has also given generously to the Conservative Party.

Any famous clients?

Too numerous to mention. Most recently he helped Mohamed al-Fayed sell Harrods to the Qatari royal family last year.