With Apple shareholder proposal pending, Carl Icahn turns his attention to Hertz

Activist investor Carl Icahn, who has a history of using his money and power to influence publicly traded companies and most recently made Apple one of his targets, is now setting his sights on Hertz, buying as many as 40 million shares in the rental car company.

Icahn's newfound stake in Hertz was revealed by an anonymous source to CNBC on Friday. The moves made by the investor prompted executives at Hertz to adopt a so-called "poison pill" earlier this week in an attempt to prevent Icahn from gaining control of the board of directors.

Prior to Friday, the identity of the activist investor was unknown. Hertz simply attributed its precautionary measures as being in response to "unusual and substantial activity" in its shares.

Icahn's stake in Hertz is said to be partially in derivatives, in addition to common stock. If his entire stake were in common stock, sources reportedly said it would make him the company's single largest shareholder.

The apparent interest of Icahn in Hertz comes as the billionaire remains involved in a public fight with the Apple Board of Directors over that company's cash and reserves. He has openly called for Apple to spend the entirety of some $150 billion it has in cash on a share repurchase program.

However, Icahn formally filed a shareholder proposal in November, in which he instead detailed a $50 billion stock repurchase plan. Apple, unsurprisingly, has recommended that investors vote against the proposal, saying that its board is already "thoughtfully considering options for returning additional cash to shareholders."

During fiscal 2013, Apple spent $23 billion of an expanded $60-billion share repurchase authorization, which contributed to combined dividend payments and repurchases totaling over $43 billion since the program was initiated some six quarters ago.

Icahn revealed in October that he had at the time 4.7 million shares of AAPL stock, up from a previous total of 4 million. His interest in the company, and stature as a Wall Street icon, have even garnered him private meetings with Apple Chief Executive Tim Cook and Chief Financial Officer Peter Oppenheimer.