The entrance to Fortress Wallenberg is an understated affair – an anonymous doorway in an old town square a short walk from Stockholm’s Royal Palace. But it is here that one of the most powerful families in Europe controls a €15 billion (£11.8 billion) business empire, including vast stakes in blue-chip companies such as Ericsson, Saab, Electrolux, ABB, Husqvarna and AstraZeneca.

The Wallenbergs rose to prominence after Oscar Wallenberg established one of Scandinavia’s biggest banks, SE-Banken, in the 1850s. Today they have interests in companies comprising 40 per cent of Stockholm stock market.

Since 1916, much of the family’s wealth has been tied up in Investor AB, a listed investment company whose chairman is Jacob Wallenberg and the biggest single shareholder is a foundation linked to his family.

“We are value investors and we qualify that by saying our model is a long-term one,” Mr Wallenberg told The Times. “We are willing to stay with a company for a very long time and we do not judge our performance on a quarter-by-quarter basis. We look at much longer time periods.”

Investor has been criticised for trading at a steep discount to its assets and also for maintaining many stakes in preferential shares which give it greater voting clout.

It would be easy to mistake Investor and the Wallenbergs as an anachronism, but it is not through conservatism or a reluctance to adapt that their wealth has endured for so long. Through the Wallenberg Foundations – charitable trusts set up in the early 19th century – the family is Sweden’s biggest funder of scientific research.

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