Based in Los Angeles, Ressler is co-founder of the private equity fund Ares Management. He married actress Jami Gertz in 1987. Mr. Ressler, 57, who co-founded the $106 billion investment firm (and is a co-owner of the Atlanta Hawks basketball team), said today that he will assume the role of executive chairman. His fellow co-founder, Michael J. Arougheti, 45, will become C.E.O. The move by Ares, which owns the likes of Neiman Marcus, is the latest sign of succession planning within the private equity industry.