He was a driving force in the creation of the American International Group (AIG), a collector of paintings by John Constable and his contemporaries, and a generous benefactor to the arts, the church and medicine.
Shortly after his birth, the family moved to Westcliff-on-Sea on the Thames estuary, a location that gave him a lifelong affection for expanses of water and sky and which he much later recalled by acquiring paintings of the area by the English painter John Wonnacott.
During his most influential years, the company grew to a force of more than 50,000 people and Manton became a leading figure in the American insurance business.
His shareholding in AIG made him very wealthy and he was ranked as the 83rd richest person in the United Kingdom according to the Sunday Times Rich List 2003.
In the early 1980s, Manton came to know Leslie Parris, deputy keeper of the British Collection at the Tate, who, together with Ian Fleming-Williams and Graham Reynolds, were the leading authorities in the field.
In creating a fund that would respond to the Tate's wish to strengthen its American collection, he was giving expression both to his affection for his birthplace and to his enthusiasm for his adopted country.
By 2005, the fund was worth $30m, and made possible the acquisition of major works by Robert Motherwell, Philip Guston, Donald Judd, David Smith, Louise Bourgeois, Ellsworth Kelly, Bruce Nauman and Cildo Meireles.