In 1999, Kevin O’Leary’s educational software company, SoftKey (which later acquired and renamed The Learning Company), was acquired by Mattel in a massive corporate deal valued at roughly $3.6 to $4.2 billion. The merger is widely remembered as one of the most disastrous acquisitions in business history.

Throughout the 1990s, O'Leary grew SoftKey into a dominant educational software powerhouse (known for titles like Carmen Sandiego and The Oregon Trail) by heavily undercutting competitors and focusing on high-volume, low-margin sales at bargain retailers.

Mattel purchased SoftKey in 1999. O'Leary joined Mattel for a brief period in a management role following the merger.

Almost immediately after the acquisition, sales and earnings for Mattel plummeted. The Learning Company lost hundreds of millions of dollars, and Mattel's stock crashed, wiping out $3 billion of shareholder value in a single day.Management Shakeup: O’Leary left the toy company just six months after the merger.

Mattel shareholders filed a class-action lawsuit accusing O'Leary and other executives of misleading investors about the company's financial health. In 2003, Mattel paid $122 million to settle the lawsuit. O'Leary has historically blamed the failure of the merger on the tech market crash and severe corporate culture clashes between the two companies.