The news of the death of Rabbi Moshe Greenberg, a religious educator who survived a brutal Gulag in Siberia and secretly taught Judaism under an oppressive Soviet regime, traveled quickly this week – from the central Israeli city of Bnei Brak, where he lived, through Germany and France to Texas and Alaska.

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The Hasidic Chabad Lubavitch movement said Greenberg died on Tuesday. He was 86 years old.

If you've traveled abroad in recent years, you've likely met one of the Greenberg family members. Although he had 17 sons and daughters, who gave him more than 130 grandchildren and great grandchildren, the rabbi rarely got to see his offspring with his own eyes, rather than through screens.

An ancient custom of Chabad members is to go on a mission in one of "Judaism's 4,000 embassies" around the globe after one's wedding.

"It began in the year 5745 (1985)," says Greenberg's fifth son, Yoske. "Our big sister Rachel settled in Austin, Texas, and has been living there ever since. A year later, our brother Yisrael founded a Chabad center on the border with Mexico. After that, we already lost count."

Anyone attempting to document the family's travels around the world will find representatives in China, Ukraine, Germany, France, New York, Ohio, California, Alaska, Michigan and many other cities and countries.

The family members speak many languages, live in different time zones, their children hardly ever see each other, and even the four siblings who still live in Israel operate Chabad centers in the cities of Lod and Beitar Illit.

"We inherited our devotion from our father, who froze for seven years in the Siberian jail because he insisted on retaining his Judaism," says Yoske from Alaska. "When the Lubavitcher Rebbe blessed me and sent me to Alaska, father told me he had frozen in Siberia and I would freeze in Alaska."

To this day, the entire family has met maybe five times, and they usually connect with each other on Skype, through letters, or a WhatsApp group called "The Greenbergs," of which all the brothers and sisters are members.

"The group chat is active 24 hours a day because of our different time zones around the globe," says Rachel.

Risked punishment to copy prayer book

Rabbi Greenberg was born to a Hasidic family in Moldavia at a time when Jews were oppressed and Jewish practices were forbidden by the Soviets, Chabad said on Thursday.

At the age of 14 he went to Tashkent in Uzbekistan to study Judaism at a secret Chabad seminary. While there, he became part of the "Chabad underground," a network that worked to maintain and teach Jewish traditions, which the Soviet's had outlawed, said Menahem Brod, spokesman of Chabad in Israel.

The Soviets banned the practice of Jewish rituals and the teaching of Judaism and those caught doing so were severely punished, Brod said. Greenberg was caught trying to escape the Soviet Union at the end of World War II and was banished to a Siberian forced labor camp for seven years.

Chabad says he kept and taught Jewish traditions in the Gulag, the infamous Soviet prison system, despite the danger.

Even with the scarce food rations and hard labor, Greenberg adhered to strict Jewish dietary laws while incarcerated, Chabad said.

The movement also recounted how in 1951, before a period of the holiest days on the Jewish calendar, Rosh Hashana and Yom Kippur, Greenberg risked punishment to copy word for word, a prayer book that had temporarily been smuggled into the camp.

Greenberg continued to clandestinely teach Judaism after his release from the Gulag and until he managed to escape to Israel in 1967.

He later recalled that he "broke down in tears" as he looked around a synagogue he was praying in and watched "in disbelief as Jews practiced Judaism openly."

In Israel, Greenberg opened a school, taught Judaism and served as director of Chabad of Bnei Brak.