Ackman Reflects on His Valeant Investment
Pershing Square's Bill Ackman

Once known as the young Carl Icahn, activist Bill Ackman has lately been struggling with his investments. The fund manager at Pershing Square Capital Management most recently apologized for his investment in Valeant  (VRX) late Wednesday, after taking a nearly $2 billion loss on the drug stock. 

Ackman, though, has an appetite for risk, and when played correctly, he ends up with a situation like his General Growth Properties  (GGP) investment. A $60-million investment in a struggling mall company garnered Ackman and his clients a $1.6 billion return. 

And his current investment in Restaurant Brands International   (QSR - Get Report) garnered Ackman's clients a 3.3% return in 2016, despite the firm's overall 12% loss on investments in 2016.

But sometimes Ackman's taste for risk goes too far. Several investments made by Pershing Square over the years have gone belly up. Here are a most contentious investments he has made. 

Editor's Pick: This story was originally published on Thursday, March 30, at 2:47 p.m.

Ackman takes a $2 billion loss on Valeant
Ackman takes a $2 billion loss on Valeant

Ackman acknowledged this troubled investment in his annual report to clients, which was released publicly Wednesday. This was after returns on the firm's main $11.1 billion fund fell 13.5% net of fees in 2016, according to the report.

"Clearly, our investment in Valeant was a huge mistake," Ackman wrote. "The highly acquisitive nature of Valeant's business required flawless capital allocation and operational execution, and therefore, a larger than normal degree of reliance on management."

Ackman added that even if the stock price had increased "very substantially," the impact on his fund's performance would not compensate for the amount of resources Pershing Square used on attempting to turn around the company.

In the end, Ackman apologized to clients for losing money on the investment.

"We deeply regret this mistake, which has cost all of us a tremendous amount, and which has damaged the record of success of our firm," he wrote.

Ackman exited his investment in Valeant earlier in March after taking a loss of about $2 billion. He remains on the board until its next election.

Ackman hangs on to stake in struggling Chipotle
Ackman hangs on to stake in struggling Chipotle

Chipotle (CMG - Get Report) was rocked this year by reports that more than 60 customers had been infected with e. coli. 

And yet, Ackman made a bet on the company. On September 6, 2016, he announced a 9.9% stake in the fast-casual Mexican grill, which was purchased at an average price of $405 per share.

For its recent fourth quarter, Chipotle's comparable store sales fell 4.8%, with a whopping 14.7% just in December alone. The company's restaurant level operating margins slipped to 13.5% from 19.6% the previous year.

While Chipotle's shares have yet to truly tank - they're hovering around $445.45 apiece (and saw a boost of more than 2% Thursday), Ackman wrote down a loss on his investment in the company for 2016.

According to his recent letter to clients, the firm took a 0.8% loss on its investment in Chipotle in 2016. 

It's no Valeant, but it is a risk, with five to 10% of customers vowing to never return to the burrito chain. 

Then there's that time Ackman took a loss on JCPenney
Then there's that time Ackman took a loss on JCPenney

Ackman invested in struggling retailer JCPenney  (JCP - Get Report) back in 2013 amid the company's makeover. After a disagreement with management, Ackman pulled his 39 million shares of the company through a sale run by Citigroup. 

In total, Ackman took a $500 million loss on the investment - he had purchased JCPenney shares at $25 apiece, and sold them for around $12.90 apiece through that Citi-led sale. 

Ackman had sat on JCPenney's board, but quit after realizing the CEO he had brought on, Ron Johnson, had set up a strategy that was driving away customers. 

Today, JCPenney still hasn't quite recovered from the huge shakeup. Shares are hovering around $6.20 apiece. 

Let's not forget Ackman's investment in Mondelez
Let's not forget Ackman's investment in Mondelez

Ackman's investment in Modelez (MDLZ - Get Report) took a loss of 1.4% in 2016, according to the letter he sent to investors. That said, shareholders saw a total return of half a percent in 2016. 

"Despite owning some of the best brands in the industry, Mondelez has among the lowest profit margins in large cap packaged food, presenting a meaningful opportunity to increase efficiency that management is currently addressing," Ackman wrote. 

There's a key point here -- Mondelez officials have to figure out how to profit from the company's packaged food, or Ackman could face a debilitating setback. 

Mondelez's full-year revenues decreased 12.5% to $25.9 billion, while fourth quarter revenues were down 8.1% to $6.77 billion. The full-year revenue decline was attributed to Mondelez's completed spinoff of its coffee business into a joint venture, called Jacobs Douwe Egberts, in which Mondelez holds a 49% stake.

Today, Ackman owns a 6.4% stake in the company. 

Herbalife: we're hedging this one, but if it bounces back, Ackman is screwed
Herbalife: we're hedging this one, but if it bounces back, Ackman is screwed

Herbalife  (HLF - Get Report) became Ackman's battleground for his famous feud against Carl Icahn. While Ackman holds a short stake in Herbalife, Icahn holds nearly 15% of Herbalife's shares. 

Ackman for years has been railing against the nutritional supplement company, calling it a pyramid scheme. He was somewhat vindicated in 2016, when the FTC issued a report that "substantially agrees" with Ackman's position. 

Despite the vindication, the legal fees Ackman has been racking up defending his position in Herbalife have been crushing. Herbalife's total shareholder return was -10.2% in 2016, according to his report. 

There is one way Ackman can be saved in terms of his Herbalife investment -- if the shares go to zero. Whether that actually happens, though, remains to be seen.