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.