TORONTO, Canada — Gregory Baum, one of Canada’s most influential and controversial theologians and a participant in the Second Vatican Council, died Oct. 18. He was 94.

Baum was the author of the first draft of “Nostra Aetate,” the Vatican II declaration that addressed the relations of the Catholic Church with non-Christian religions.

After being admitted to St. Mary’s Hospital in Montreal Oct. 8, he told a friend, “I’m disappearing inside.” He decided not to continue the dialysis treatment that had kept him alive for the last four years.

As a young theologian, Baum shot to prominence in the early days of Vatican II. He was mentored by Cardinal Augustin Bea, then-president of the Pontifical Council for Promoting Christian Unity. An ally of St. John XXIII, Bea went looking for credible Catholic experts on Catholic-Jewish relations and found his man in Baum.

Baum was born to a Jewish mother and Protestant father in Berlin in 1923. At 17, in 1940, he came to Canada as a war refugee after a brief stay in England. Among the many Jewish refugees in camps in Quebec were young intellectuals who set up classes for the younger refugees, which Baum attended.

He became a Catholic during the war years and joined the Augustinian order in 1947. He was ordained a priest in 1954. He studied theology at the University of Fribourg in Switzerland and published That They May Be One, an influential book about Catholic ecumenism, in 1958.

His involvement in the Second Vatican Council began even before the world’s bishops met in Rome, as Vatican officials were planning the church’s first truly global meeting.

“I remember the first session I attended was in November 1960,” Baum told Canada’s The Catholic Register in 2012. “I was at the first session of the secretariat in Rome. We had the first meeting with Cardinal Bea and Monsignor (later Cardinal Johannes) Willebrands, and this was all about ecumenism. At the end of the meeting Cardinal Bea said, ‘I just saw the pope and he said to us, he said that he wants the secretariat to prepare a statement to rethink the church’s relationship to the Jews.'”

John XXIII’s concern about the 6 million Jews killed in the heart of Europe during World War II largely drove the Second Vatican Council. Baum had already begun publishing in academic journals about Catholic-Jewish relations.

Baum attended all three sessions of the council as a peritus, or theological expert, consulting on “Nostra Aetate”; the Decree on Ecumenism; and the Declaration on Religious Freedom.

After the council, Baum taught theology and ethics at the University of St. Michael’s College in the University of Toronto. He left the priesthood in 1974 and married. He studied sociology at the New School for Social Theory in New York and, in the 1980s, taught in the religious studies department at McGill University, Montreal.

Baum was a frequent target of conservative campaigners in English Canada and the United States. Monsignor Vincent Foy, a Canadian theologian, published frequent articles condemning Baum as a “Marxist … ex-priest.” Foy popularized a theory that Baum had excommunicated himself by marrying before his laicization was formally recognized by the Vatican. Baum’s opinions on ordination of women and gay marriage drew frequent criticism.

Baum’s critics were further incensed when he published his 2016 autobiography, “The Oil Has Not Run Dry,” in which he spoke of his first homosexual experience, at the age of 40.

The author of more than 20 books, Baum said he was never worried by the criticism.

“I live in a dream world in Quebec,” he told The Catholic Register. “I still belong to a wide network of progressive Catholics. I never meet any conservatives.”

He was founder and editor of the influential journal The Ecumenist from 1962 to 2004. The journal highlighted connections between theology and sociology, politics and culture. In his retirement he became outspoken on Quebec politics, multiculturalism and economics.

Swan is associate editor of The Catholic Register, Toronto.