Shares of the El Segundo, California, company slipped in Monday morning trading.
The company said longtime board member Christopher A. Sinclair will replace Stockton as chairman and interim CEO.
"Mattel is an exceptional company with a great future but the Board believes that it is the right time for new leadership to maximize its potential," Mr. Sinclair said in a statement. "We are committed to delivering improved growth and financial performance and remain confident in our ability to leverage our unmatched portfolio of brands, global scale and strong balance sheet as we execute on our strategic plan. I look forward to engaging with the entire Mattel community as we work to deepen our connections with children and parents through expanded product innovation and improved retail execution. We will be working during the coming months to revitalize the business and to identify the right leadership for Mattel as it enters its next phase of growth and value creation."
Mr. Sinclair continued, "On behalf of the Board and everyone at Mattel, I sincerely thank Bryan for his many valuable contributions over the past 15 years in expanding our business and portfolio of brands and building our executive team."
The toy maker also disclosed that its net income tumbled 59 percent to $149.9 million from $369.2 million in the three months that ended Dec. 31. On a per-share basis, Mattel earned 44 cents per share in the most recent quarter, or 52 cents per share not counting hits from integration costs and taxes.
Revenue fell 6 percent to $1.99 billion.
Analysts forecast, on average, earnings of 91 cents per share on $2.14 billion in revenue, according to the data firm FactSet.
Mattel has struggled for several quarters now with slumping sales of its iconic Barbie dolls.
Making matters worse, late last year, Barbie lost its top spot on the crucial holiday wish lists of girls to merchandise from the Disney hit "Frozen." The National Retail Federation's Holiday Top Toys Survey found that one in five parents, or 20 percent, planned to buy "Frozen" merchandise for their girls. That beat the 16.8 percent that are looking to make a Barbie purchase.
Stockton became CEO in January 2012 and then was named chairman a year later. Sinclair said in a statement from the company that the Mattel board believed it was the right time for a change in leadership to maximize the company's potential.
Mattel will announce full results from its quarter on Friday.
The company's stock fell 45 cents, or 1.6 percent, to $27.60 in Monday morning trading after falling as low as $24.88 earlier in the session, while broader indexes slipped less 1 percent. Mattel shares are coming off a year in which their price sank 35 percent, while the broader Standard & Poor's 500 index climbed 11.4 percent.