"briefly, I find that I like being involved in leading change and driving the business more directly," Lehman, who is 55, said in a statement. He returns to his old job on Wednesday and has resigned from Sun's board.
And, will become executive vice president of finance. "He will be with us for the foreseeable future," Sun spokeswoman Stephanie Von Allmen said. "He's been convinced to stay on as EVP of finance."
Though the Santa Clara, Calif.-based company has been, Lehman said the arrival of new server, software and storage products "leads me to believe Sun can deliver more value to customers than HP, IBM and others combined."
Sun President Jonathan Schwartz hailed Lehman's move. "It is great to see a senior statesman like Mike join the team," he said in a statement.
Related changes also took place at Sun's board. Lehman resigned from his position there at the same time Robert Finocchio joined. Finocchio, a former chief executive of database company Informix and former president of networking company 3Com Systems, also is on the board of Altera, CaseCentral, Echelon, Intransa and Silver-Peak Systems.
Although Finocchio won't take Lehman's role as chairman of the board's audit committee, he will be a member of that committee and qualifies as a financial expert in auditing, Sun said.