Harel moved to Palestine in 1930 and spent five years working on a kibbutz before establishing his own orange-packing company.
The Jewish state of Israel was established on 14th May 1948 when the British mandate over Palestine came to an end. David Ben-Gurion became prime minister and the following month he ordered Harel to sink the Irgun Zvai Leumi ship Atalena off the Tel Aviv coast.
In 1952 Harel was appointed head of Mossard and five years later overall chief of Israeli's secret services. He worked closely with the CIA and provided the Americans with valuable information on the Soviet Union. He also took part in organizing a dirty tricks campaign against Mapam, the Israeli left-wing political party.
A strong opponent of Gamal Abdel Nasser, Harel established the Trident Network in 1957. This involved Mossard working closely with the secret services in Iran and Turkey against the government in Egypt. He also armed Iraqi Kurds and built airfields in Turkey and Ethiopia with CIA money.
Harel was also responsible for trying to capture Nazi war criminals. In 1960 Mossard agents led by Harel captured Adolf Eichmann in Argentina. He was kidnapped and for nine days was interrogated by Harel in one of Israel's safe houses. Heavily sedated he was brought to Israel on an airliner disguised as a sick passenger. Eichmann was found guilty of "crimes against the Jewish people, crimes against humanity, and war crimes" and was executed on 31st May, 1962.
Harel's agents were also responsible for murdering German scientists working in Egypt. Complaints were made by diplomats from Federal Republic of Germany and in March 1963 David Ben-Gurion sacked Harel as head of Mossard. The right-wing in the Kesset supported Harel and in June 1963 Ben-Gurion was forced from office.
Harel served as special adviser to the prime minister, Levi Eshkol (1965-1966) and served one term in the Knesset (1969-1973).
Isser Harel died in Israel on 19th February, 2003.