Case, who stepped down as chairman in 2003, was one of the original architects of the merger of AOL (search) and Time Warner, which helped erase more than $200 billion in shareholder value from the stock and was the target of two government probes into its accounting.
Once viewed as an albatross to the owners of the Warner Brothers (search) movie studio, HBO and Time Inc., AOL has emerged over the past year as the center of attention for top Internet companies looking to buy a stake in the division.
"I strongly believe that AOL, once the leading Internet company in the world, can return to its past greatness," Case said in a statement. "Over the past few months, I have been pleased to see a renewed focus on AOL at Time Warner, and the emergence of so many strategic alternatives."
Although AOL continues to lose millions of dial-up Internet subscribers every year, the company made more of its programming available freely over its Web properties to attract online advertising.
Case said he was leaving to devote more time to his new company, Revolution, which provides health-care and wellness programming and services.