As befits the most powerful woman in Silicon Valley, Sheryl Sandberg cuts to the chase. Her dark eyes fix you during questioning. Then the answer is fired back: rat-tat-tat-tat. An hour of conversation can shrink to 40 minutes with ease. When you are effectively running an internet business worth $100bn (£63.2bn) there isn't much time to waste. Mark Zuckerberg may be the public face of Facebook, but Sandberg, as chief operating officer, is the closest the social media sensation has to a corporate suit.
When we met last year, Sandberg was warm, but defensive, testing the swivel on her chair as she listened intently. Might she deviate from her theme or speculate on something else entirely? Those dark eyes firmly conveyed the message: not likely.
It is this unspoken, steely resolve that has marked Sandberg out as a high-flier. If Facebook is to live up to the lofty price tag it gained when the shares were listed on Wall Street yesterday, it will be because investors are willing to put their faith in the vision of Zuckerberg, but the delivery of Sandberg. For Zuckerberg, who met the 42-year-old at a party four years ago just as he was on the hunt for a business brain to steer his empire, Sandberg might just be his best hire. With the fresh challenge of navigating Wall Street, she could prove to be his best friend too.
The mother-of-two came highly recommended. At Google, she helped to create the search advertising business that is at the heart of the Google money machine. Prior to that, at the age of 29, she was made chief of staff to Larry Summers, when he was US Treasury Secretary during Bill Clinton's presidency. Summers hired her first at the World Bank after she stood out in the economics class he taught at Harvard.
Speculation last year suggested Sandberg could have been heading back to Washington, but this time as the boss. She was said to be on a list of candidates to succeed Tim Geithner, the current Treasury Secretary. Such is her stature that few blinked an eye at the idea.
"She could have any job in the world," said one close friend, who thinks that, despite her soaring reputation, she will hang around at Facebook for a few more years.
That should be enough time for the odd-couple partnership of Sandberg and Zuckerberg to flourish. He is 14 years her junior and a relative introvert. He dropped out of Harvard, while she got an MBA. She is a polished performer who has championed women in the workplace and pushed philanthropic causes to the fore. While Zuckerberg favours a hoodie and jeans, Sandberg sports designer threads.
Friends say that despite agreeing to float the business he dreamt up in a Harvard dorm room eight years ago, Zuckerberg is still on a mission to increase the scale and scope of Facebook. So far it has 900 million-plus users, with the one billion mark in reach.
Zuckerberg's ambition doesn't necessarily chime with generating the growing sales and profits that Facebook's new investors will demand. Sandberg and David Ebersman, the company's finance director, have been handed that task.
When she agreed to quit Google to become Zuckerberg's number two, Facebook had already taken off, but how it made money wasn't apparent. Sandberg instilled a sense of drive in the company, and embraced corporations that were keen to harness social media to get young people talking about their brands. That charm offensive helped revenues of $350m in 2008 mushroom to $3.7bn last year.
It wasn't just about bumping up sales, though. Sandberg's operational flair had to preserve what Facebook stood for while managing a huge expansion in staff numbers. That has included the opening of offices around the world and moving its HQ from a cramped former Hewlett-Packard building on to a larger campus.
There was also a period of instability following the departure of several of Zuckerberg's earliest cohorts. She has been to Facebook what Eric Schmidt has been to Google – a steadying hand that helped the company grow up. The company's only missteps have been over its privacy controls, and those fears seem to be in abeyance for now.
Schmidt remains a great fan of Sandberg's, even if relations between the two companies grew frosty after she poached several people from Google's senior team.
"I'm old", she exclaimed to the crowd at Facebook's marketing conference in New York earlier this year, in a string of jokes that subtly underscored her role as the "adult supervision" to the company's youthful founder. Or if not supervision, exactly, at least a wise adviser. Zuckerberg asked her whether he should expect his midlife crisis at 40 years old, or at 30. She was, she notes, 42 at the time: "That's 12 years ago. That's the sort of question that's going to ruin my day," she recalled.
"I'm old and I remember a time before the internet," she went on, saying she remembered going to the library to look up information. "There are people who don't know what a card catalogue is – and I've chosen to work with all of them."
Sandberg describes Facebook as a "platform company". This platform has drawn in many users, and anyone who wants to reach them is welcome to build on top of it – at a price, inevitably. It means that Facebook can be everywhere, without actually investing in all directions. It influences newspaper readership, for example, by letting users recommend articles to their friends. Media agencies suggest that up to 20 per cent of internet users arrive at a news story via social media. If a story goes viral, it can reach 40 per cent.
"We want to work with every newspaper in the world to help your users make the experience of interacting with your content more viral, more social, more personal," Sandberg said last year. "But we are not going to go produce news ourselves."
The core to Facebook's success is convincing advertisers that users will tolerate commercial messages while they are checking up on the latest news and pictures from their friends and family. It helps that brands have set up Facebook pages aplenty and are driving customers there instead of to their corporate websites.
"I feel quite comfortable being dependent on advertising because I think it is a great business for us," Sandberg added. "We are in the growing part of the market. People had thought you could only do brand building on TV, but that is not true, you can build a brand on Facebook. People are doing it."
It isn't as though she hasn't got enough on her plate. Facebook has come a long way, but it must still work harder to emulate Google's level of profit, which is still 10 times that of its younger rival.
As well as her full-time role, Sandberg sits on the board of Disney. In January, she cemented her position as one of the world's best-connected businesswomen by co-chairing the World Economic Forum in Davos, the annual snow-capped talking shop for world leaders. While there, she carried out an interview with Christine Lagarde, the head of the International Monetary Fund.
But even Sandberg betrayed a need to slow down when she quit a non-executive role at Starbucks to concentrate on the Facebook flotation.
Her responsibilities are a far cry from an unremarkable childhood in Miami, growing up as the daughter of an eye doctor. Now she juggles the demands of a home life shared with her husband, internet entrepreneur David Goldberg, and their children. Things change, however. Pushed on one point when we met, she refused to be pinned down.
"There is no always here," she said. "We don't live in a world of always."
Investors buying into Facebook expecting Sandberg at the helm in the long term would do well to remember that.
A Life In Brief
Born: Sheryl Kara Sandberg, 28 August 1969, Washington DC
Family: Daughter of Joel, an ophthalmologist, and Adele. Married to David Goldberg, CEO of SurveyMonkey; they have two children.
Education: Studied economics at Harvard, and took her MBA there.
Career: Worked for Larry Summers at the World Bank, then at the US Treasury Department, before moving to Google. She has been chief operating officer of Facebook since 2008, and is on the board of Disney.
She says: "There's no such thing as work-life balance. There's work, and there's life, and there's no balance."
They say: "Sheryl is creating new opportunities, removing obstacles and making a real difference in others' lives." Muhtar Kent, chairman of Coca-Cola Company