Stephen Hemsley, the chief executive who oversaw extraordinary growth in more than a decade running UnitedHealth Group, is leaving the job next month and will be succeeded by Dave Wichmann, the company’s president.

As an insurance company, UnitedHealthcare under Hemsley has taken advantage of growth opportunities in the Medicare program, which introduced prescription drug benefits via private health plans in 2006.

Following Optum’s high-profile rescue of the federal government’s HealthCare.gov website in 2013, company officials have talked about taking a bigger role in overseas health care markets, including the possibility of contract work in the United Kingdom.

“While Stephen Hemsley has been an iconic CEO and these are big shoes to fill, in our view the company will continue successfully along its game-changing path of shaping health care in America and beyond its borders, with no change expected in the strategy,” Ana Gupte, an analyst with Leerink, wrote in a note to investors.

“That’s critical to us,” she wrote, “that Steve, who made the transition from ‘the guy who makes the trains run on time’ to the single most visionary health care executive we know ... is staying on in that strategic role.”