Billionaire hedge fund manager Carl Icahn has amassed a sizable stake in health insurance industry giant Cigna Corp. (CI) and plans to vote against its proposed $54 billion acquisition of Express Scripts Holding Co. (ESRX) when shareholders vote Aug. 24, as first reported by The Wall Street Journal. (See also: Icahn Slashes Stake in Herbalife.) Icahn, a controversial, high-profile activist investor who once served as an advisor to President Trump, holds less than a 5% stake in the insurance company.