Andrew Witty — who became UnitedHealth Group's CEO in 2021 — is stepping down from the top post due to personal reasons after years leading large health care companies.

During the tail end of Witty's time as CEO of UnitedHealth, the company's stock price reversed from growing to receding, as the company navigated a major cyber attack, investigations and the brutal killing of its insurance arm's leader.

Witty's rise in healthcare began when he joined GlaxoSmithKline, maker of many drugs and Sensodyne toothpaste, in 1985. He climbed the ranks and became CEO of the British company, now known as GSK, in 2008.

Under Witty's leadership, the company undertook a large reorganization and expensive deals and partnerships, including a project with Pfizer in 2009 to launch a company focused on HIV treatment and care.

Witty holds the title of "Sir" after being knighted in 2012 due to his service to the United Kingdom's economy.

But Bloomberg reported that leader faced criticism for GSK's sluggish financial performance and a pipeline dry of promising medicines near the end of his tenure.

In 2016, Witty announced he planned to retire from GSK the following year, saying in a news release, "GSK is a very special company with an inspiring mission and many dedicated people. By next year, I will have been CEO for nearly ten years and I believe this will be the right time for a new leader to take over."

The retirement was short-lived.

Witty joined UnitedHealth first as a director in August 2017 and then took over Optum, the company's fast-growing health care services division, as its chief executive officer in July 2018, according to a filing with the Securities and Exchange Commission.

During his first quarterly investors call leading Optum, Witty emphasized the importance of digital health for the company's future. In a statement announcing the Optum leader as UnitedHealth's president in late 2019, then-CEO David Wichmann said Witty clarified the division's strategy as it made remarkable progress.

The additional job title meant Witty was now in charge of overseeing UnitedHealth business strategy formulation and development.

But the COVID-19 pandemic caused a change of plans. The company announced in spring 2020 that Witty would temporarily leave the company to help the World Health Organization to promote development of a coronavirus vaccine.

After returning to UnitedHealth, Witty said at an annual investing conference in Dec. 2020 that no "country's health care system has ultimately been sufficiently robust to be able to withstand and react." He emphasized the need for UnitedHealth to focus on data and technology to create the "best value-for-money health care system we can," the Star Tribune reported.

Several months later, Witty was named chief executive of UnitedHealth Group. The timing confused analysts, the Minnesota Star Tribune reported, as Witty had only recently returned from WHO. But by the end of 2021, the company posted an annual profit of $17.3 billion.

UnitedHealth's momentum slowed in 2024, as it faced massive obstacles. Witty's pay declined 34% to $16.4 million.

Witty's first costly obstacle came when the group announced in February 2024 that its Change Healthcare business in Tennessee was the victim of a major cyberattack, which was eventually understood to have affected the data of roughly one in two Americans. Then in December, the killing of Brian Thompson, the leader of UnitedHealth Group's insurance arm, captured the attention of the world and focused intense attention on how often it denies health care claims.

In a video message, Witty called the murder "immeasurably sad" and "profoundly shocking," encouraging employees to look out for themselves.

"This is a moment where, in among everything else, we're reminded of the fragility of families, of individuals and the importance that that really represents," Witty said.

Just months later, Witty is leaving the role of CEO with no explanation other than unstated "personal reasons." He will remain with the company as a senior adviser.