Carl Icahn ended his months-long effort to block Michael Dell's $25 billion offer to take Dell private. The activist investor, the company's second-largest shareholder, said that a war with the billionaire founder and the company's board "would be almost impossible to win."

His withdrawal significantly improved the odds that the company would finally muster enough votes at a special shareholders' meeting on Thursday.

"The Dell board, like so many boards in this country, reminds me of Clark Gable's last words in "Gone with the Wind," they simply 'don't give a damn,'" Icahn wrote in a letter to shareholders on Monday.

Dell and private equity firm Management Silver Lake Partners wants to take the company private to transform it away from public scrutiny into a provider of enterprise computing services. Icahn argued that Michael Dell's offer undervalued the company's shares.

Icahn said that his involvement meant the shareholders got additional value for their shares, forcing Michael Dell and Silver Lake to raise their offer.