Rabbi Elyashiv has died in Jerusalem after battling heart, lung and kidney complications for months. He was 102.
Tens of thousands of devoted followers are expected to attend his funeral due to be held as soon as possible.
Elyashiv was the leader of the Lithuanian (non-Hasidic) branch of ultra-orthodox Judaism, known for its extreme piety and committment to the study of the Torah and Talmud (Jewish laws). Elyashiv continued this conservative tradition when he became leader and his pronouncements were considered law by hundreds of thousands of Jews in Israel and the diaspora.
From his modest home - one and half rooms - in Mea Shearim, Jerusalem, he decided who was a Jew, who could convert, how Jews could marry and how they could divorce, what would happen to the Israeli economy in the fallow year (once every seven years, as decreed in the Bible) and what the government policy would be on organ donations.
In the arena of rabbinical law - the halacha - he was very strict and uncompromising. He saw the halacha as a closed code that could not be damaged at any price, even in the name of pragmatism or flexibility in adapting to a social or national reality.
He also wielded considerable political power through the ultra-religious Degel Hatorah party in the Knesset and in a surprise move ordered it to back Israel's withdrawal from Gaza in 2005.
He was descended from a long line of rabbis and emigrated to Jerusalem at the age of 14, during the British Mandate of Palestine, from eastern Europe.
He and his late wife, Sheyna-Haya, a daughter of Rabbi Arieh Levin, had 12 children. In May 2009, he saw the start of the sixth generation of his descendents, with the birth of a grandson to one of his great-grandchildren.