Johannes Cardinal Willebrands, Requiescat in pace.

The Hague - Cardinal Johannes Willebrands, a key figure in the Roman Catholic Church's efforts to improve relations with other Christians and Jews, has died at age 96.

Willebrands was known at the Vatican as "The Flying Dutchman" for his travels promoting Christian unity. He died Tuesday night, the Dutch Catholic Church announced Wednesday.

As president of the Vatican's Commission for Religious Relations with the Jews, Willebrands long sought to improve troubled relations between the faiths. He also was mentioned as a possible candidate for the papacy at the two conclaves of 1978.

In the 1980s, he called for more Jewish teachers at Catholic theological institutes to expand the study of Judaism.

Willebrands was named president of the Vatican's Secretariat for Promoting Christian Unity in 1969 and held the post for 20 years. The secretariat was renamed the Pontifical Council for Promoting Christian Unity by Pope John Paul II in 1988.

"I especially value him as a bishop who before, during and after the Second Vatican Council worked energetically and expertly for the restoration of Christian unity," said Dutch Cardinal Adrianus Simonis, who succeeded Willebrands as Archbishop of Utrecht and chairman of the Dutch Bishops Conference.

Prime Minister Jan Peter Balkenende, in a letter to Simonis, described Willebrands as "a tireless bridge builder" between Catholics, other Christians and Jews.

Dutch bishops also praised his efforts to promote church unity, saying, "Many non-Catholic church leaders will today remember a partner in ecumenical discussions and a personal friend."

One of nine children of a Dutch auctioneer, Willebrands became a priest in 1934. Considered a gifted student, he was sent to Rome to study at the Angelicum Pontifical University. He was named a bishop in 1964 by Pope Paul VI.

Willebrands served as Archbishop of Utrecht from 1975-1983. During that time, Dutch Catholics struggled with a growing rift between conservatives and liberals and an increase in secularization.

After retiring from that position, he moved back to Rome, where he continued to serve as president of the Pontifical Council for Promoting Christian Unity until his 80th birthday.

His health failing, Willebrands moved in 1997 to a convent in Denekamp in the eastern Netherlands, where he was tended by Franciscan nuns until his death.

Funeral arrangements were not immediately announced. (Thanks to AP for this obituary.)