Nine people who were hired to whip young millionaire founders into shape before the company got too big

It’s not hard to find startups led by 20-something founders in Silicon Valley.

But as the startups start to grow into multi-billion-dollar companies, even the most talented tech wunderkinds often need a seasoned executive partner who can provide “adult guidance” at some point down the road.

These 9 people were hired by some of the biggest tech companies to provide that type of counsel to a less experienced founder.

Eric Schmidt had a rocky couple years when he first came in as Google's CEO

Eric Schmidt was hired as Google CEO in 2001, taking the job that was held by Google co-founder Larry Page.

Schmidt's hire was orchestrated by John Doerr, the Kleiner Perkins partner who had made it a pre-condition to his $US12.5 million investment in Google.

Page and fellow Google co-founder Sergey Brin apparently didn't agree with the hire at first, making bitter comments about Schmidt early on. But after seeing Schmidt lead the company to years of growth and profitability, they started to appreciate him -- later calling Schmidt's hire 'brilliant.'

Sheryl Sandberg helped Facebook find better ways to make money

Sheryl Sandberg was hired as Facebook COO in 2008. At the time, she was already a star executive at Google, having led its advertising business as VP of Global Online Sales and Operations.

When Sandberg first joined Facebook, it was seeing slowing member growth, and didn't have a sustainable business model yet. Under Sandberg, Facebook set up a solid ad model that now generates billions of dollars.

Carol Bartz succeeded Jerry Yang as Yahoo CEO to be the 'smart, tough-love adult'

When Carol Bartz was brought in as CEO in 2009, Yahoo was a company under lots of pressure, especially from investors who were upset it didn't take Microsoft's acquisition offer.

Bartz's hire was initially seen as a smart move at the time, just the type of 'tough-love adult' executive Yahoo sorely needed. After all, she had a good track record of turning around ailing companies, including her last company, Autodesk.

But Bartz failed to revive Yahoo's fortunes, and eventually was fired in 2011. In her first interview post-Yahoo, Bartz said, 'These people f -- ed me over.'

Before Marc Benioff, Salesforce was led by a guy named John Dillon

Many people think the Salesforce CEO position was always filled by its co-founder Marc Benioff. But there was a two year period, from 1999 to 2001, when a guy named John Dillon was brought in to lead the company as CEO, while Benioff was Chairman.

According to some early Salesforce investors we spoke with previously, Benioff wasn't seen as the right person to be CEO at the beginning. So the board hired Dillon, a former Oracle and Hyperion executive to provide better guidance.

But Dillon and Benioff didn't get along well, and eventually one of them had to go. Dillon was eventually shown the door, and he's now CEO of a company called Aerospike.

Paypal mafia member David Sacks doesn't have to work anymore, but he signed on to work under Zenefits CEO

Yammer CEO David Sacks at Launch Festival 2013

David Sacks joined the HR software startup Zenefits last December. Former PayPal COO and founder of Yammer, the company Microsoft bought for $US1.2 billion, Sacks technically doesn't have to work any more, much less under someone.

But he decided to become a Zenefits employee in December, and work for its 34-year old CEO Parker Conrad. 'Zenefits was honestly the most exciting company that I've seen that needed my help,' he told Business Insider in a previous interview.

Dan Levin joined Box as COO and helped its young leadership team take the company public

Box COO Dan Levin joined the company in 2010, when its leadership team, led by CEO Aaron Levie and CFO Dylan Smith, were in their mid-20s.

Levin, who cut his teeth in various roles at Intuit, immediately turned the young company into a more robust, structured organisation.

And finally, earlier this year, Box completed its much-anticipated IPO, turning itself into a $US2 billion enterprise file storage juggernaut.

The first major move Dropbox made after raising money at a $10 billion was to hire Dennis Woodside as COO

Dropbox COO Dennis Woodside

The first major move Dropbox made after raising $US350 million at a $US10 billion valuation early last year was to hire Dennis Woodside as COO, making him the #2 guy behind CEO Drew Houston.

Woodside started his career as an M&A lawyer, before spending nearly a decade at Google as its head of advertising.

As Dropbox COO, Woodside is reported to have turned the young company into a much more structured organisation, hiring experienced managers across the board. He's also known for being a brutally direct manager, according to former employees.

Emily White joined Snapchat but left after 16 months, as CEO Evan Spiegel wanted to be more hands-on

When Emily White was brought into Snapchat as its COO in December 2013, it was seen as a smart move similar to what Facebook did with Sheryl Sandberg -- a seasoned, female executive providing guidance to a 20-something wuderkind CEO.

White was best-known for setting up an advertising model at rival photo-sharing service Instagram, and was expected to help Snapchat's then 23-year old Evan Spiegel grow the company.

But she recently left Snapchat, after only 16 months, as Spiegel sought to be 'more hands-on,' according to Re/code. It's unclear what her next move is going to be.

Marne Levine was hired as Instagram's first COO last year

Marne Levine, the 44-year old, former VP of global public policy at Facebook, was hired as Instagram's first COO in 2014. She spent about four years at Facebook, largely overseeing the company's overseas expansion.

Levine's job involves managing day-to-day operations, including HR, communications, and policy issues, while helping the relatively inexperienced Instagram cofounders expand the product globally.

Levine is also on the board of Sheryl Sandberg's Lean In organisation.

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