Question: What Hamilton, Bermuda based holding company who formerly featured CEO John J Byrne?

Context paragraphs:
John J. Byrne: John J. Byrne (July 11, 1932 – March 7, 2013) was an American longtime insurance industry executive who was CEO of GEICO, White Mountains Insurance Group and Fireman's Fund.  He also served as chairman of Overstock.com.

Maiden Holdings: Maiden Holdings Ltd., (NASDAQ: MHLD ) is a Bermuda based holding company with insurance subsidiaries that provides specialty reinsurance products for the global property and casualty market.  The company has operating subsidiaries in the United States (Maiden Re, Maiden Specialty), Europe (Maiden International), and Bermuda (Maiden Insurance).

Somers Limited: Somers Limited is an investment holding company based in Hamilton, Bermuda.  Its shares are traded on the Bermuda Stock Exchange.

Bigfoot International: Bigfoot International, Inc. was a New York City based holding company, which developed email communications, marketing automation and customer interaction software products during the dot-com era.  Founded in 1997 by Lenny Barshack and James Hoffman, it grew out of Bigfoot.com, a free e-mail provider and Web directory.  It eventually developed into a group of three subsidiaries: Bigfoot.com, email marketing company Bigfoot Interactive and browser/CRM software company Neoplanet, Inc.  The company ended in 2000.

International Navigation Company: The International Navigation Company (INC) was a Philadelphia based holding company owning 26 ships totaling 181,000 tons and carried more passengers than either Cunard or White Star, when the company was reorganized as International Mercantile Marine in 1902.  INC was formed in 1871 with the backing of the Pennsylvania Railroad to operate foreign flagged vessels on transatlantic routes to Philadelphia.  Clement Griscom, the company’s general manager, entered into an agreement with the Belgian Government to establish the Red Star Line to operate a mail service out of Antwerp to Philadelphia and New York.  This subsidiary would provide most of the company’s profits for the next 30 years.

White Mountains Insurance Group: White Mountains Insurance Group () ) is a financial services holding company based in Hamilton, Bermuda.

Tambour (company): Tambour (Hebrew: טמבור‎ ‎ ) is an Israeli company engaged in the manufacture of paint, coatings and advanced construction materials.  The company was founded in Palestine by 1936.  In 2014, Singaporean based holding company, Kusto Group, has acquired Tambour.

John Charman: John R Charman (born 1953) is an English businessman, who has made his career in insurance.  He is currently CEO and chairman at Bermuda based Endurance Specialty Insurance Ltd.

Canadian Breweries Limited: Canadian Breweries Limited was an Ontario based holding company in the brewery industry.  In 1969, the company was sold to Rothmans, and is now called Carling O'Keefe, with its brands currently owned by the Molson Coors Brewing Company.

John Curtin House: John Curtin House Limited is a Canberra based holding company owned by the Australian Labor Party, named after John Curtin House, a building in Barton in Canberra which previously housed the headquarters of the Australian Labor Party.  The building is in turn named after the World War II-era Prime Minister and ALP member for Fremantle 1928-1945, John Curtin.

Supporting paragraphs: John J. Byrne White Mountains Insurance Group
Answer: White Mountains Insurance Group