NEW YORK (Reuters) -Brian Thompson, the CEO of UnitedHealth's insurance unit, was fatally shot in midtown Manhattan last week in what police described as a targeted attack by a masked assailant lying in wait just before the parent company's annual investor conference at a Hilton Hotel.

Authorities arrested Luigi Mangione, 26, in Altoona, Pennsylvania, in connection with the shooting on Monday. Mangione was found with a "ghost gun" - a firearm assembled from parts, making it untraceable - and a silencer consistent with the weapon used to shoot Thompson, New York City Police Commissioner Jessica Tisch said. 

Thompson, 50, had been with the company for 20 years and was CEO of UnitedHealthcare, the large insurance unit of UnitedHealth Group, since April 2021. The following is what you need to know about UnitedHealthcare:

WHAT IS UNITEDHEALTHCARE'S BUSINESS? 

UnitedHealthcare is the largest U.S. health insurer, providing benefits to more than 50 million Americans. The company provides benefit plans that pay for much of routine healthcare as well as care for customers who fall ill or get injured. The unit had $281.4 billion in revenue in 2023, nearly double that of the next largest U.S. health insurer. Americans routinely pay more for healthcare than people in any other country.

HOW DOES IT FIT INTO UNITEDHEALTH GROUP?

UnitedHealth Group is a $560 billion health conglomerate that consists of two main subsidiaries. In addition to the insurance business that was led by Thompson, there is Optum, which includes a pharmacy benefits manager, specialty pharmacy, data analytics and doctor and surgical practices.

It also includes technology company Change, which was the target of a cyber attack this year that impacted thousands of providers and millions of healthcare customers.

The whole company brought in $371.6 billion in revenue last year and had over 440,000 employees at the end of 2023. Sir Andrew Witty became CEO of UnitedHealth Group in 2021 after having run Optum. He was previously CEO of Britain-based pharmaceutical company GSK from 2008 to 2017.   

HOW MANY PEOPLE DOES UNITEDHEALTHCARE COVER AND WHERE?

The company provided health insurance for more than 50.6 million at the end of the third quarter, including 49.3 million people across the United States. Nearly 30 million are enrolled in employer-based or other commercial insurance, 15.3 million in government-backed Medicare plans primarily for those age 65 and older under Medicare Advantage programs, and 4.3 million in Medicaid plans for low-income people. The company's global business provides benefits to customers in over 150 other countries, according to its annual report.

Under Thompson, UnitedHealthcare grew the number of people it covers domestically, which rose from around 44 million people when he took over as CEO in April 2021. 

HOW PROFITABLE IS IT?

In 2023, the insurance business earned $16.4 billion, up nearly a third from 2020, the year before Thompson took over as CEO.