(Bloomberg) -- Igor and Dmitry Bukhman built one of the world’s largest mobile-game developers over the past two decades. Now they’re ramping up plans for the billions they’ve made from their entertainment empire.

The Playrix founders’ personal investment firm, which manages about $4 billion, is moving into its first permanent office in London’s glitzy St. James’s district with staff set to roughly double in number since the start of the year to about 10 employees, according to a person with knowledge of the matter.

The brothers have recently sought to hire a new head for their family office, Rix Capital, as well as senior investment and legal staff, the person said, asking not to be identified as the details are private. 

Igor, 41, and Dmitry, 37, whose firm makes games including Township and Gardenscapes, are together worth about $11 billion, according to the Bloomberg Billionaires Index.

A Playrix representative didn’t respond to a request for comment.

The Russian-born Israeli entrepreneurs — who live in London – have rapidly built up their investments outside Dublin-based Playrix, which employs more than 3,000 people worldwide and saw its number of users boom during the pandemic.

Rix Capital is now among the world’s biggest family offices, the lightly regulated investment firms for the ultra-wealthy that have surged in number globally over the past two decades. Family offices for single fortunes manage about $1 billion on average, according to 2022 research from Campden Wealth.

The brothers got their start in Russia during the early 2000s, when Igor learned from a university professor that he could sell software online. Along with Dmitry, who was in high school at the time, he gave it a try. In 2004, when the business reached $10,000 in monthly revenue, they registered as a legal entity and rented office space in the basement of a book warehouse.

Playrix moved its headquarters to Ireland about a decade ago and closed its operations in the brothers’ homeland and Belarus last year following Russia’s invasion of Ukraine. Playrix was the world’s third-largest mobile game publisher by revenue in 2022, according to marketing agency Udonis.

The Bukhmans are Playrix’s majority shareholders and never raised outside money to help finance their firm. They started ramping up their personal investments over the past five years through dividends from the gaming firm, according to the person with knowledge of the matter. Rix Capital was established in late 2021 through Playrix executives, according to regulatory filings.

Rix typically allocates capital across asset classes including private equity, hedge funds and fixed income, as well as listed stocks, the person said, asking not to be identified because the information isn’t public. The firm is expected to complete the move into its new London headquarters in the next few months.

Other members of the world’s rich, including branches of Egypt’s Mansour dynasty and Canada’s Weston family, have also set up family offices in London, a global hub for wealthy individuals partly due to its access to luxury homes, business opportunities and private hospitals.

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