Mr. Zuckerberg hired Ms. Sandberg in 2008 — when the company was still known as Facebook — to become its first chief operating officer. She oversaw Facebook’s initial move into digital advertising, courting big brands and small businesses to expand it into a multibillion-dollar endeavor.

Ms. Sandberg became one of the highest-profile female executives in the business world, eventually writing a best-selling book, “Lean In,” about her experience.

But she also faced criticism during one of Facebook’s most tumultuous periods. Russians manipulated the company’s platforms to spread misinformation in the 2016 U.S. presidential election, and its privacy and data-collection practices drew regulatory scrutiny.