Old Mutual Plc's Julian Roberts is stepping down as chief executive officer of Africa's biggest insurer and will be replaced by Standard Bank Group Ltd.'s Bruce Hemphill. Roberts, 57, is resigning after almost seven years leading the London-based company, and will stay on until the fourth quarter of this year, Old Mutual said in a statement Wednesday. Hemphill, 51, head of wealth, insurance and non-bank financial services at Standard Bank in Johannesburg, will be an executive director of Old Mutual and based in London until he takes over, it said.