"As the co-founder of AOL, I continue to have a special pride and passion for AOL, and I strongly believe that AOL -- once the leading Internet company in the world -- can return to its past greatness," Case said in a statement.
Case sold AOL to Time Warner at the height of the technology bubble, only to watch it all melt down into a shadow of its former corporate self.
In his resignation statement, Case noted that he remains one of Time Warner's largest shareholders and said he will be actively engaged "as strategies for AOL's future are considered, and as steps are taken to maximize Time Warner shareholder value."
Case said the decision to leave the Time Warner board will increase his ability to grow Revolution LLC, his new firm. Revolution has been acquiring firms in the technology and health fields.
Case has signed up a list of luminaries for Revolution's board of directors including former U.S. secretary of state Colin Powell, former Hewlett-Packard CEO Carly Fiorina, and former Netscape CEO Jim Barksdale.
"Leaving Time Warner's Board will give me a greater opportunity to grow Revolution, including avoiding any potential conflicts of interest as Revolution moves into new areas," Case said.