Mark Zuckerberg hired Sheryl Sandberg as Facebook’s chief operating officer in 2008 as the social network was growing fast and trying to attract investment. Zuckerberg, who founded Facebook in his Harvard dorm room, was just 23 – Sandberg, then 38, was deemed “the adult in the room”.

The former sales executive at Google and chief of staff at the US Treasury rose to become one of the most influential figures in global technology sector and one of very few women at the top of the industry. She also made a lot of money – after selling most of her stake in Facebook’s parent company, Meta, which also owns Instagram and WhatsApp, she is now worth close to $2bn (£1.6bn).

Sandberg, now 54, left that role a year and a half ago and on Wednesday night she announced she was leaving Meta’s board too. “This feels like the right time to step away,” she wrote in a Facebook post, as Meta was “well-positioned for the future”.

“Thank you Sheryl for the extraordinary contributions you have made to our company and community over the years,” said Zuckerberg, the world’s sixth-richest person with an estimated $133bn personal fortune. “Your dedication and guidance have been instrumental in driving our success and I am grateful for your unwavering commitment to me and Meta over the years.”

Sandberg was one of six executive officers named in the prospectus when Facebook filed for an initial public offering in 2012. With her exit, only Zuckerberg remains of the six. She had been seen as so critical to the success of the company that she was named alongside the founder as one of the key personnel who posed a potential risk to investors money if they were to leave.

Zuckerberg and Sandberg met at a Christmas party at the home of Dan Rosensweig, a Silicon Valley executive in 2007. “We talked for probably an hour by the door,” Zuckerberg told the New Yorker. They went on to have twice-weekly dinners at Sandberg’s house, often until she had to kick him out at midnight. Dave Goldberg, Sandberg’s late husband, said it was like Sandberg and Zuckerberg were “dating”.

“What do you believe? What do you care about? What’s the mission? It was very philosophical,” Sandberg said of the late night chats. Describing her role at Facebook, Zuckerberg has said she “handles things I don’t want to. All that stuff that in other companies I might have to do. And she’s much better at that.”

That “stuff” included developing an advertising strategy to make the company hundreds of billions a year in revenue and hiring and firing employees. She also handled political and ethical issues, dealing with scrutiny over the Cambridge Analytica breach, the January 2021 attack on the US Capitol and the documents leaked by the whistleblower Frances Haugen that revealed some of the platform’s most toxic impacts.

The run of scandals during Sandberg tenure prompted activists to call for her resignation and question her legacy as a women’s rights advocate. Shaunna Thomas, the co-founder of women’s rights group UltraViolet, has said that under Sandberg’s watch, Meta platforms became “a rightwing playground where misogyny, racism, disinformation” proliferated.

“Sheryl Sandberg may fancy herself a feminist, but her decisions at Meta made social media platforms less safe for women, people of colour, and the American electoral system,” Thomas said. “Sandberg had the power to take action for 14 years, yet consistently chose not to.”

However, Debra Williamson, an analyst at Insider Intelligence who has been following the company since its founding, said: “There have been plenty of controversies surrounding Meta, but from a purely business standpoint, what she built at Facebook is pretty powerful, and will go down in the history books.”

Sandberg testified in front of Congress in 2018 to answer for Facebook’s missteps and allegations of voter manipulation in the 2016 election, and again in 2021 to deflect blame from the company for its role in the Capitol riots – acting as a softer and more personable foil to Zuckerberg.

As well as effectively running one of the world’s largest technology companies, she has also found time to write two books. 2013’s Lean In: Women, Work, and the Will to Lead became an international bestseller and established Sandberg as a leader in female empowerment.

“What we realised is that in order to really get to equality, equality in leadership everywhere, from our parliaments to our statehouses to our homes, we’re going to have to go younger,” she said last year. “Who wants to say to a girl seven years before she enters the workforce, ‘One day you’re going to be in a meeting and some man is going to talk over you, voice something you just said and get credit for your ideas.’”

Her second book, Option B, is “about facing adversity, building resilience, and finding joy” and focuses on her husband’s death. “I was in ‘the void’,” she wrote, “a vast emptiness that fills your heart and lungs and restricts your ability to think or even breathe.”

Sandberg will now spend more time working with a foundation she set up to focus on women’s issues in the workplace, and “build a more equal and resilient world”. However, there is speculation that the committed Democrat may be planning an entry into politics. Recently she has spoken out against abortion bans, given $3m to the American Civil Liberties Union and campaigned against sexual violence in the Israel-Gaza war.