John Riazzi, principal, managing director and CEO of Transamerica Investment Management, resigned, he confirmed in an e-mail. He will leave the firm in June and intends to start his own firm. Mr. Riazzi, who is based in Dayton, Ohio, will be replaced as CEO by Gary Rolle, Transamericas principal, managing director and CIO, who is based in Los Angeles. Mr. Rolle will remain CIO for growth equity strategies. Michelle Stevens, a principal, managing director and portfolio manager based in Dayton, will take on additional responsibilities as value equity CIO, according to Mr. Riazzi. Calls to Transamerica officials were not returned by press time.