Few Jews today would not have heard of Lubavitch, but when Rabbi Nachman Sudak came to the UK in 1959, its name would have drawn a blank for most. He was one of the early disciples of Rabbi Menachem Mendel Schneerson, the last Lubavitcher Rebbe, who transformed Chabad from simply one Chasidic sect among many to an international outreach Jewish movement.

Rabbi Sudak, who had been smuggled out of Russia to Israel as a young boy, was sent here by the Rebbe as his shaliach (emissary) to the UK. "Today, if you want to be a shaliach, you go to a corner of a suburb," says Rabbi Shlomo Levin of South Hampstead Synagogue, "In those days, you were given a country."

A shy man who never sought the limelight, Rabbi Sudak was unwavering in his devotion to the cause. Under his tutelage, Lubavitch grew in the UK from a small community to a network encompassing schools, 25 Chabad houses and 11 campus centres across the country, while its graduates have filled many synagogue pulpits.

But the whole enterprise of trying to draw in young Jews who were becoming estranged from their religion was novel at the time, even outlandish.

"Anglo-Jewry was still in the throes of the post-war years," recalled Bentzion Rader, a friend of Rabbi Sudak who has been active in the movement for 50 years. "Outreach was a new word, scorned by many who now embrace it."

Rabbi Sudak attracted a wide range of students to his talks, building a base of support. "Despite his own perceived lack of fluency in English," Mr Rader said, "his acknowledged mastery of his subject compensated more than adequately."

His colleagues admired his depth of knowledge of Lubavitch philosophy and his activism became apparent early on when, as a yeshivah student in New York, he published works by the Rebbe.

Such was the regard with which he was held that the Rebbe referred to him as "My Nachman". He was appointed to the umbrella body for the worldwide movement in 1991.

It was a recognition of how far Lubavitch had come when in 2000 he was made an OBE. His industry and dedication ensured that the UK branch was able to overcome crises, no more so than when it stared insolvency in the face seven years ago. "When his back was against the wall, that's when he was at his strongest," Rabbi Levin said.

Rabbi Sudak, he said, was "very much a black-and-white person, there weren't shades of grey. That was part of his strength."

The Sudaks became the premier family in UK Lubavitch: Rabbi Sudak's wife Fradel is executive head of its primary schools, his son Rabbi Bentzi is its current chief executive.

Emeritus Chief Rabbi Lord Sacks, who attributes his own entry into the rabbinate to an encounter with the Lubavitcher Rebbe, said that Rabbi Sudak had turned Lubavitch "from a marginal presence to one that affected tens of thousands of lives and changed the entire tone of Anglo-Jewry".