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.

New Positions in Cigna, AmTrust, and Others

Icahn is known as an activist investor. While it's difficult to say whether or not any given position in the billionaire's portfolio could be the target of activist maneuvering, there are at least three major companies representing new positions in Icahn's portfolio during the second quarter of the year. The billionaire bought up a massive stake of 18.42 million shares of AmTrust Financial Services Inc (AFSI), as well as 2.38 million shares of Dell Technologies (DVMT). Other significant purchases include a new position in Cigna (CI) amounting to just over 500,000 shares. Besides these, Icahn also entered into stakes in VMWare Inc. (VMW) and Energen Corp. (EGN) to the tune of 2.27 million shares and 5.19 million shares, respectively.

Reduction in Cheniere

Icahn sold off a portion of his stake in Cheniere Energy Inc. (LNG), although he retains a sizable position in the energy company. Going into the second quarter the billionaire held 32.68 million shares, but by the end of that three-month period he had just 23.68 million shares, meaning he sold off about 9 million shares over the quarter.

Herbalife Saga Continues

About five years ago, Icahn and hedge fund rival Bill Ackman had a lengthy and bitter feud about nutrition company Herbalife. Ackman put the company down as a "well-managed pyramid scheme," while Icahn referred to Ackman as a "liar." Over time, Icahn has been the investor to apparently come out on top in this particular fight. He continued to supplement his holdings in HLF stock, buying up new shares last quarter.

The information presented above is available via Icahn's 13F filing with the U.S. Securities and Exchange Commission. All hedge funds and other institutions managing more than $100 million are required to submit 13F reports each quarter. For investors tracking these filings to get a sense of where the biggest money managers invested, however, it's important to keep in mind that the 13F filings are at least a month and a half out of date, and that investors like Icahn may have drastically shifted their positions since this data was documented. Further, 13F filings only show a partial picture of a firm's holdings.