Brian Thompson spent more than 20 years climbing through the ranks at UnitedHealthcare, one of the nation’s largest health insurers and a main division of the conglomerate UnitedHealth Group, and there were no signs that his ascent was slowing.

He had been chief executive of the insurance division since 2021, overseeing a period of substantial profits. The division reported $281 billion in revenues last year, providing coverage to millions of Americans through the health plans it sold to individuals, employers and people under government programs like Medicare. The division employed roughly 140,000 people.

During his tenure, the company’s profits rose, with earnings from operations topping $16 billion in 2023 from $12 billion in 2021. Mr. Thompson received more than $10 million in salary and compensation last year.

He was well-respected by Wall Street analysts, where he was known for his reassuring description of the company’s outlook.

Those who worked with him during his oversight of the company’s government programs in Medicare and Medicaid said he was responsive to concerns about how to best serve the individuals in those programs. “Every interaction with him felt extremely genuine,” said Antonio Ciaccia, a consultant who discussed using pharmacists to help provide better care for people receiving Medicaid. “He was a very good listener.”

On a recent call with Wall Street analysts and investors to discuss the company’s financial results, Mr. Thompson provided a confident voice when questioned. When asked about the employer segment, he told one analyst, “I feel really good about not only our performance, but our cost management inside our commercial business.”