The investor owns 11.4% stake in Forest and successfully agitated for change in a bruising battle with the company's previous management.
Someone who bought Forest shares on November 16, 2009 - coincidentally the date that Icahn's investment was first made public - and kept the stock until now would have realized a total return of 209% vs 84% for the S&P 500.
Over the period, Forest's market cap increased by almost $17B, a jump of over 193%.
"We believe that our activism did much to help bring about the great result," Icahn says.
However, he laments, Forest could have realized even more value had it listened to him from the get-go and not forced him to fight proxy battles.