White Mountains Insurance Group

White Mountains Insurance Group (NYSE: WTM) is a holding company with business interests in property and casualty insurance, and reinsurance. The group owns reinsurer Sirius and a 75% stake in specialty insurance carrier OneBeacon. It is based in Hanover, New Hampshire.It is owned by Jack Byrne who in 1985 was invited to run the troubled Fireman's Fund, then a subsidiary of American Express.