Karen Lynch

When Lynch became Aetna’s first female president in early 2015—a role CEO Mark Bertolini held before her—the four-year vet assumed responsibility for 95% of the health insurer’s $60.3 billion in revenues. It’s been a busy year for Lynch: In August Aetna announced plans to withdraw from many of the state Obamacare exchanges, accounting for some 5% of the company’s sales. A bigger deal: Aetna’s proposed acquisition of Humana, which would nearly double its revenues but which faces a tough legal challenge from the Justice Department.