Bill Gates’ relationship with his first money manager wasn’t a particularly successful one.

In the mid-1980s, the Microsoft co-founder entrusted management of his growing fortune to Andrew Evans, a close friend who ran a brokerage firm.

The pair had known each other since Microsoft’s early days, bonding over their love of sports cars and hot technology stocks. Evans described the relationship as “one of the most important friendships” in his life.

Despite this, their professional ties came crashing down after a newspaper exposé in 1993 revealed Evans had spent time in prison for bank fraud years earlier. Gates, who had visited his friend when he was behind bars, did not need the attention.

The US government had started to sniff around allegations of anti-competitive behaviour from Microsoft, and Gates was months away from getting married. He parted ways with Evans shortly after.

Given the history, it is hardly surprising that the management of Gates’ immense fortune since then has been designed to attract as little attention as possible.

Cascade Investment, the vehicle that handles much of the Microsoft founder’s estimated $143bn (£101bn) wealth, is bigger than most hedge funds, but has no website, and is based in a nondescript office building on the outskirts of Seattle.

Its employees are discouraged from having a social media presence, and investors that have worked with Cascade on deals say it does as little as possible to attract attention.

“In many ways, Cascade could not be more boring, other than its affiliation with Bill Gates,” says Michael Finke, a professor at the American College of Financial Services.

But Gates’s recently announced divorce from his wife of 27 years, Melinda French Gates, combined with reported sexual harassment allegations in 2017 against Michael Larson, the billionaire’s longtime confidant who runs Cascade, have put a spotlight on the way Gates’ fortune is run.

Larson, 61, a former bond manager who grew up in Albuquerque – the New Mexico city where Gates founded Microsoft in 1975 – was hired after a scrupulous background check, only being told who he would be working for after 13 references were grilled by a recruiter. After he was hired by Gates, he was told to be conservative, and avoided the limelight (the name Cascade was chosen because it was as generic as it gets in the waterfall-heavy Pacific north-west).

Despite the source of Gates’ wealth, and the dotcom boom in internet shares in the second half of the 1990s, Cascade made a decision to stay out of tech.

Roger McNamee, a Silicon Valley investor who had handled some of Gates’ technology investments, said Larson was concerned about Gates’ wealth becoming concentrated.

“Bill and Michael made a policy change – no more investments in tech,” says McNamee, who describes Larson as “exceptionally modest … and very, very smart”. The modesty extends to having almost no public presence.

The result has been a string of safe, value-based bets. Cascade describes itself as providing “patient, long-term capital”, with stakes in public shares, bonds and real estate.

Only a handful are disclosed: it is the biggest shareholder in tractor maker John Deere, with a 9.3pc stake worth $11bn, as well as Canadian National Railway, the North American freight giant, and the US car dealer AutoNation. It owns stakes in Virgin Media owner Liberty Global and, in 2007, teamed up with Saudi Prince Alwaleed bin Talal to buy the Four Seasons hotel chain.

Cascade has also made Gates America’s biggest private owner of farmland, buying up around 242,000 acres across 19 states, according to a recent analysis by US magazine The Land Report. These purchases, which can cost hundreds of millions of dollars, are often made under other names. When Gates was asked in a recent online Q&A why he was buying up so much land, he shrugged that “my investment group chose to do this”.

In the UK, it has owned stakes in Carpetright, the distribution giant Bunzl and security company G4S, as well as a brief period part-owning the luxury hotel company Cliveden.

Most recently, it teamed up with Blackstone to take over FTSE 250-listed private jet operator Signature Aviation in a £3.5bn deal.

Cascade does not reveal its returns, and its conservative approach has won plaudits for weathering the financial crash better than most funds. However, a 2014 report suggested that Cascade’s returns would have been similar if it had simply kept Gates’ money invested in Microsoft, in the same way that tech billionaires such as Amazon’s Jeff Bezos and Oracle’s Larry Ellison have done. Since then, Microsoft’s shares have risen by 400pc, suggesting the billionaire would have been better off never selling a share.

“Since value stocks have had a rough decade, my sense is that Cascade’s investments have probably not outperformed the market or other more aggressive private equity strategies,” says Finke.

Larson has no licence to be aggressive, however. Cascade is managing money that will fund Gates’ philanthropy. Both Gates and his soon-to-be ex-wife have pledged to donate 95pc of their wealth to the Bill and Melinda Gates Foundation.

Divorce, however, has complicated things. When the couple announced their split on May 3, it appeared harmonious, revealed in simultaneous and identically worded tweets. The couple said their joint work at the foundation would continue.

Subsequent allegations have presented a less amicable picture. Days after the announcement, The Wall Street Journal revealed that Melinda had met divorce lawyers two years earlier, after Gates’ ties to Jeffrey Epstein became public. Last week, the newspaper reported that Gates’ departure from Microsoft’s board last year came after an inquiry into an affair 20 years earlier. Gates’ spokesman said his departure had nothing to do with the affair.

Sources speaking to The New York Times also said Melinda was concerned about how Gates had dealt with a sexual harassment claim against Larson. According to the report, in 2017 Larson had allegedly harassed the manager of a bike shop that a Cascade-funded venture capital firm had invested in. The woman reportedly settled, with Larson reinstated after an internal review. Cascade has declined to comment on the claims.

Although both have promised their money will eventually end up with the foundation, Melinda is splitting her finances from the Microsoft billionaire. In less than three weeks since their divorce was announced, Cascade has moved around $4bn of shares to Melinda. The true value is likely to be higher, since only movements in companies where Cascade has a significant stake must be disclosed.

The details of the couple’s divorce settlement are not public, but dividing up the giant fund is likely to have been a complex process, says Laurie Pawlitza, a divorce lawyer. “It really becomes like a corporate deal. Sometimes you try to spread things out over a couple of tax years, because it’s more efficient.”

Melinda, meanwhile, has devoted more attention to Pivotal Ventures, her own investment company, set up to promote social issues and gender equality. With her wealth being separated from Gates, she may now have the firepower to pursue that goal more aggressively.