John XXIII, who will be made a saint along with John Paul II at the Vatican, is credited with saving thousands of Jews during the Holocaust and opening the door to Judeo-Christian dialogue, Baruch Tenembaum told AFP in an interview at the Foundation's New York headquarters.
The Italian-born John XXIII, whose given name was Angelo Giuseppe Roncalli, "did such extraordinary things. I'm delighted that he is becoming a saint, even if -- as a Jew -- beatification doesn't affect me."
"He couldn't have done more than he did," explained Tenembaum, a 80-year-old Argentine known for his efforts to improve inter-faith dialogue.
In 2009, his name was placed in the running for the Nobel peace prize.
As the Vatican's envoy to Turkey from 1935, John XXIII helped save the lives of thousands of Eastern European Jews facing persecution from the Nazis, including by giving Hungarian Jews baptismal certificates.
"At the time, having identity papers labeling you a Catholic was enough to save your life," Tenembaum said.
A document on file at the Yad Vashem Holocaust memorial in Israel cites the future pope as being "among the most sensitive to the Jewish tragedy and most vigorous in rescue efforts".
Tenembaum has asked that Yad Vashem add John XXIII to its list of "Righteous Among the Nations" -- a title honoring non-Jews who showed courage to protect Jews during the Holocaust.
The International Raoul Wallenberg Foundation honours the legacy of a Swedish diplomat, posted to Nazi-occupied Budapest in July 1944, who is believed to have saved tens of thousands of Hungarian Jews in the final months of the Holocaust by providing them with protective passports.
The foundation works to preserve his legacy and that of others who saved numerous lives, and not only during the Shoah.
Tenembaum has worked hard to publicize John XXIII's work during his time in Turkey, about which there are few official records.
The scholar also praised John XXIII -- nicknamed "Good Pope John" -- for helping open up the Roman Catholic Church to dialogue with other faiths during his 1958-1963 papacy.
Less than three months after being elected pope, John XXIII announced preparations for the Second Vatican Council, a global gathering of Catholic bishops, which opened in October 1962 and proved to be revolutionary, in that it finally acquitted Jews of Christ-killing.
He was the first to put a stop to the use of the word "perfidious" to describe Jews in Good prayers, Tenenbaum said.
During his time as a Vatican envoy to France, the soon-to-be-saint played a key role in plans for the partition of Palestine and the creation of the state of Israel.
According to diplomats involved in the negotiations, he helped persuade Pope Pius XII to remain silent, effectively allowing mainly Catholic countries to vote on the partition plan free of Church influence.
"Roncalli's attitude definitely had something with do with the creation of the state of Israel. If the Vatican had given the order to vote against it, they would have voted against it," Tenembaum said.
Tenembaum says he current Pope Francis, a fellow Argentine, seems to be following in the path of John XXIII.
"Since the time of Pope John XXIII, I think the pope that most resembles Roncalli is Francis, at least from what we've seen so far," Tenembaum said.