Michael Dell made news last Friday when he announced he and his investment partner, Silver Lake Partners, had sweetened their offer for Dell (UNKNOWN:UNKNOWN), the company he founded and still leads. A day before that announcement, noted investor Carl Icahn, who opposes Michael Dell's plan, had increased his own stake in Dell by purchasing an additional 4 million shares, according to a Monday SEC Form 4 filing.

Icahn's most recent purchase brings the total number of Dell shares owned, directly or indirectly by he and his affiliated investment companies, to 156,478,650. Icahn's 8.9% ownership stake makes him the largest non-insider owner of Dell's shares.

The purchase price for Icahn's 4 million Dell shares was $12.94 each, according to the filing. As of this writing, shares are trading at $13.72. They closed Thursday at $12.96.

Michael Dell and investment firm Silver Lake Partners' latest buyout bid is $13.75 per share, with stockholders also receiving a special dividend of $0.13 per share. Icahn is opposed to the offer. A shareholder vote on the offer is scheduled for Sept. 12.

-- Material from The Associated Press was used in this report.