Avery Cardinal Dulles was one of the greatest thinkers in the modern Roman Catholic church and perhaps its most distinguished representative in the United States. The first American Jesuit to be named a cardinal, and for his last two decades a professor at Fordham University, New York, he was acknowledged to be the dean of American Catholic theologians.

His influence, however, extended far beyond the US. He was a prolific writer and lecturer, whose work ranged from studies of John Henry Newman and Pope John Paul II to original essays in ecclesiology and explorations of the theology of revelation and of faith. Few modern theologians have thought so deeply or so productively about the nature and purpose of their discipline and its role both in the Church and in the world.

Avery Robert Dulles was born in 1918 in Auburn, upstate New York, into the old northeastern US Establishment — a class of privilege, Protestantism, and stern New England duty. His family was not conspicuously wealthy but from its 17th-century origins among the Puritans and down to Dulles’s day, it had enjoyed a kind of complete self-assurance, a perpetual confidence about its place and its duty in the world. Behind the family members stood the elite boarding schools and Ivy League universities, weekends on sailboats, grand tours of European capitals, the house on Long Island, the summer place upstate, the Navy, the foreign service.

Avery Dulles’s looks betrayed those origins. Tall and spare, he was a lanky man with a large square chin, thin lips, and prominent eyebrows over sharp, inquisitive eyes. And from those Establishment origins he chose the unlikely path of conversion in 1940, while a student at Harvard University, to what was, in those days in the US, very much the lower-class religion of Catholicism.

After wartime service in the US Navy, in which he rose to the rank of lieutenant and won the Croix de Guerre for his work as liaison to the Free French, he joined the Society of Jesus in 1946. In 2001 he was elevated to the cardinalate, his red hat a tribute to what he had achieved in the intervening half century.

By the time of death, from the after-effects of the polio that he had contracted during the war, Dulles had published more than 700 theological articles and 23 books, becoming, along the way, the most important American Catholic theologian of the 20th century.

Dulles’s great-grandfather, John Watson Foster, had been President Harrison’s secretary of state. His great-uncle, Robert Lansing, was President Wilson’s. His father, John Foster Dulles, was President Eisenhower’s. His uncle, Allen Dulles, led the CIA from 1953 to 1961. His aunt, Eleanor Dulles, was an influential State Department officer and Washington hostess.

The Establishment of which Dulles’s family was a member reached its peak during the Cold War, but it stood on the shoulders of earlier establishments, particularly the long line of Protestant ministers who had preached Calvinism to America since the days of the nation’s beginning.

Dulles’s grandfather, Allen Macy Dulles, was a Presbyterian pastor and co-founder of the American Theological Society. His father, John Foster Dulles — coming to believe that only the gospel and international organisation could preserve world order — first found wide notice as an expert on international affairs by chairing a 1941 peace commission for the Federal Council of Churches.

Still, Avery Dulles described himself as an agnostic and materialist when he arrived at Harvard as an undergraduate in 1936. The subsequent decade saw many prominent Catholic conversions in the US, particularly intellectual and literary ones. But even for his intellectualised generation, Dulles had a conversion that was curiously cerebral. It began when, as an undergraduate, he became convinced that Catholic versions of philosophy offered more complete accounts of the world than other philosophical systems. Acceptance of the philosophy drew him to acceptance of the theology, which in turn drew him to acceptance of the faith — except, of course, that intellectually accepting the need for faith is not the same as actually having faith.

But then, in 1939, “one grey February afternoon”, in Harvard’s Widener Library, as he wrote in his conversion memoir, A Testimonial to Grace (1946), “I was irresistibly prompted to go out into the open air . . . . The slush of melting snow formed a deep mud along the banks of the River Charles, which I followed down toward Boston . . . . As I wandered aimlessly, something impelled me to look contemplatively at a young tree. On its frail, supple branches were young buds . . . . While my eye rested on them, the thought came to me suddenly, with all the strength and novelty of a revelation, that these little buds in their innocence and meekness followed a rule, a law of which I as yet knew nothing . . . . That night, for the first time in years, I prayed.”

By 1940, his first year in Harvard law school, Dulles was ready to be received into the Catholic Church. He founded the St Benedict Centre, an independent Catholic evangelising organisation in Boston, and he fell, briefly, under the spell of Father Leonard Feeney, SJ, a charismatic street preacher later involved in controversy over his strong views of the eternal damnation of all who are not explicitly baptised members of the Catholic Church.