The billionaire investor's 13F filing reveals new investments during Q2. : For billionaire investment titan Carl Icahn, the second quarter of the year was a busy one. According to a filing submitted to the SEC earlier this week, Icahn increased his stake in troubled nutrition company Herbalife Nutrition Ltd (HLF) as well as his own namesake Icahn Enterprises LP (IEP), per a report by Proactive Investors. Below, we'll explore some of the other shifts that the billionaire made to his holdings in the previous quarter. Icahn is known as an activist investor.