Michael Dell made news last Friday when he announced he and his investment partner, Silver Lake Partners, had sweetened their offer for Dell (DELL.DL), 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.