When Carl Icahn buys, Wall Street pays attention.

Icahn is known for affecting what is known as the "Icahn lift" -- a bump in a company's stock price that often occurs after he has taken a position in it. And while the swing is sometimes temporary, Icahn has the numbers to prove that his involvement has a long-term impact as well.

In an "activist manifesto" the billionaire investor penned for The Economist in 2014, Icahn laid out his case for activist investing and how and why his brand of it works. "The reason our record is so strong is that we are 'activists' in the truest sense of the word," he wrote. "Over the past two decades we have got actively involved with CEOs and boards, often in a friendly fashion."

And Icahn's active involvement has paid off. According to Icahn, a person investing in 23 companies whose boards his appointees joined from Jan. 1, 2009, to June 30, 2014, would have obtained an annualized return of 27%.

"Over the decades, our activism has enhanced shareholder value for all shareholders by multi-billions of dollars," he wrote.

Of course, not all of his activist bids are successful, nor are all of his investments made with an activist push. But his buys are always interesting to watch.

Here are four stocks Icahn has been buying lately, according to his most recent 13F corresponding to June 30, 2016.

Allergan 

AGN Chart AGN data by YCharts

Icahn's only new stake of the second quarter is Allergan (AGN) . As of the end of the period, he owns 3.4 million shares valued at $785.7 million, giving the company a 3.9% allocation in his holdings.

The billionaire in May revealed he had acquired a "large position" in the Botox maker and expressed his support for CEO Brent Saunders, who he worked with at Forest Labs (which was acquired by Actavis, which subsequently merged with Allergan). "We have every confidence in Brent's ability to enhance value for all Allergan shareholders," he said.

Allergan is a specialty pharmaceutical company that engages in developing, manufacturing and distributing generic, brand and biosimilar products. It has a $100.3 billion market cap and trades at a P/E of 20.47.

Allergan is a holding in Jim Cramer's Action Alerts PLUS charitable portfolio. "We view Allergan as a buy, at current levels, for anyone with a minimum eight- to 12-month investment horizon, as it will take time for the company to grow into its full and fair valuation," wrote Cramer and Research Director Jack Mohr on Friday.

Xerox

XRX Chart XRX data by YCharts

Icahn bumped up his stake in Xerox (XRX) last quarter and as of June 30 owns 99 million shares worth $939.8 million. The company has a 4.6 allocation in his public equity portfolio.

Icahn first disclosed his Xerox position in November of last year, calling the company "undervalued." And earlier this year, he revealed that he had upped his holdings even more in the wake of news Xerox was to split. He lauded the announcement, and his backing of the company, in a series of tweets.

1/4 Happy to announce we reached an agreement with $XRX re: separation into two independent public companies: https://t.co/KoRmzNkzTb

    — Carl Icahn (@Carl_C_Icahn) January 29, 2016

2/4 We believe the separation will greatly enhance value for $XRX shareholders

    — Carl Icahn (@Carl_C_Icahn) January 29, 2016

3/4 I applaud and respect Ursula Burns for doing what she believes shareholders want - as @Donahoe_John did with $EBAY and $PYPL

    — Carl Icahn (@Carl_C_Icahn) January 29, 2016

4/4 I hope and believe the results will be just as good for $XRX shareholders

    — Carl Icahn (@Carl_C_Icahn) January 29, 2016

Xerox provides business process and document management solutions worldwide. It has a $9.9 billion market cap and trades at a P/E of 23.88.

Icahn Enterprises

IEP Chart IEP data by YCharts

Icahn upped his position in his namesake company Icahn Enterprises (IEP) to 123.6 million shares valued at $6.7 billion as of the end of the second quarter. It comprises 32.9% of his portfolio.

Icahn Enterprises, through its subsidiaries, operates in investment, automotive, energy, metals, railcar, gaming, food packaging, real estate and home fashion businesses in the U.S., Germany and internationally. Its investment segment operates various private investment funds. It has an $8.3 billion market cap.

AIG

AIG Chart AIG data by YCharts

AIG (AIG) is another increased stake for Icahn last quarter. He ended the period with 44.6 million shares worth $2.4 billion. It has an 11.9% allocation in his public equity holdings.

The billionaire had been engaged in a high-profile activist battle with AIG, calling for the bailed-out insurer's breakup. The company headed off what appeared to be an impending proxy fight in February by agreeing to give board seats to Icahn and fellow activist shareholder John Paulson.

AIG provides insurance products and services for commercial, institutional and individual customers in the U.S., the Asia Pacific and internationally. It has a $63.5 billion market cap.