Emilio Bot?n is a billionaire Spanish banker renowned for running a tight ship. He asks that his top credit officers at Santander ? one of Europe?s largest banks ? make a trek to his vacation home each summer to report on loan exposures. And he queries the head of his charitable foundation, euro for euro, on its smallest donations.

Yet, there is one not-so-small matter that Bot?n (pronounced bo-TEEN) has failed to keep tabs on: A Swiss bank account secretly opened long ago by his father that grew to such a size that when Spanish authorities discovered its existence last year, Bot?n and other family members paid 200 million euros (about $273 million) in taxes to avoid tax evasion charges.

At the request of tax fraud inspectors, a Spanish national court is investigating whether the payment is enough, given the amount that was stashed abroad; tax experts in Spain say that the account could reach two billion euros.

The court has also said officials need more time to sift through the blizzard of documents that the family submitted and will consider whether a criminal charge of document fraud should be brought.

A lawyer for the Bot?ns, Jes?s Rem?n, said the family was cooperating with the investigation and was ?fully in compliance with its tax obligations following their voluntary filing? last year. He added that no family member had been charged with wrongdoing.

Bot?n?s tax problems come as debate intensifies over whether struggling governments should demand more tax revenue from the rich. On Monday, President Obama called to end some tax breaks for the wealthiest taxpayers.

Last Friday, the Spanish government reintroduced a wealth tax that it had abolished three years earlier, hoping to collect an estimated 1.08 billion euros from taxpayers with more than 700,000 euros in declared assets. Spain?s wealthiest have so far not publicly endorsed calls for higher taxes, and Bot?n on Friday told reporters that ?it seems to me very bad to reintroduce? the wealth tax.

More so than in other European countries, where bankers are largely anonymous figures, Bot?n holds sway in Spain. Although he avoids social events, his influence is seen as wide-ranging. And he has been able to retain control of Santander despite his family?s controlling just 2% of its shares. Neither the judiciary nor the family has provided details about how much money the Swiss bank account contained or how the amount grew over time. Nor would Rem?n, the lawyer, comment on whether Bot?n had been aware of the account.

What is known is that Bot?n?s father, also called Emilio, left Spain with part of his wealth in late 1936, after the start of the Spanish Civil War, fearing, like many other Spaniards, what might come.

The elder Bot?n spent a few months in London before moving to Basel, Switzerland, and eventually returning to Spain to resume leadership of the bank that he had run since 1933. But while he returned to Spain, the money he salted away in Switzerland did not. The senior Bot?n died in 1993. Representatives for Bot?n have said that the family has voluntarily paid what it owes and that Bot?n expects that the government will agree and close the case. It seems altogether likely that Bot?n and his family will be cleared of any wrongdoing, which would come as no surprise to the banking patriarch?s fiercest critics.