Bermuda-based Arch Capital Group Ltd. said John Rathgeber, CEO of a reinsurance unit, was also named as the subsidiary's chairman.

Mr. Rathgeber's appointment at Arch Reinsurance Co. became effective on March 1, the company said yesterday in a Business Wire statement. Tim Olson, previously the unit's chief underwriting officer, was promoted to president and chief operating officer, according to the statement.