In a television interview years later he recalled how he informed Ben-Gurion of the outcome of the successful operation: "I have brought you a present…Eichmann is here."

In 1963 Harel quit as Mossad head after a bitter dispute with Ben-Gurion over how to best deal with German scientists developing missiles for Egypt. Two years later he was appointed as adviser on intelligence affairs to Ben-Gurion's successor as prime minister, Levi Eshkol, but he retired shortly afterwards.

"To Isser, the guarantor of the honor, the security, and the secrets of the state," was the inscription written by Ben-Gurion on the photograph he gave him during their historical reconciliation and farewell meeting in 1966.

Born in Vitebsk, Russia, in 1912, Harel immigrated to Palestine in 1931. An agricultural worker and one of the founders of Kibbutz Shefayim, he joined the Haganah in 1942, serving as a policeman until becoming head of Haganah intelligence in 1944.

With the creation of the Israel Defense Force at the end of the War of Independence, Harel became one of its first lieutenant-colonels, and was appointed as head of the General Security Services (Shin Bet). In 1952 he became head of Hamossad Hamercazi Lemodi'in Ubitahon (The Central Institute for Intelligence and Security), the Mossad, which he headed until 1963.

During all those years, even his wife and neighbors had no idea what Harel's job really was. His wife, Rivka, never asked superfluous questions. Many of his acquaintances eventually found it difficult to believe that this diminutive man (known as Isser the Little, in distinction to Isser Be'eri, the former chief of military intelligence, who was nicknamed Isser the Big) was Israel's chief spy, who personally planned and executed the Mossad's most daring espionage activities.

Harel won international recognition for his professional talent and cold, analytical mind. His only hobbies were opera and detective novels. He had no sense of humor and was easily offended, and yet he was highly respected and even feared.

During the early 1950s Harel kept a close watch on Communists and Mapam left-wingers, some of whom were suspected of collecting classified information. There can be little doubt, however, that Harel's major contribution to Israeli security during this period was overseeing the arrest of a number of spies like Aharon Cohen and Kirt Site, who operated on behalf of Eastern European Communist regimes.

The most important of his cases was the arrest of Dr. Israel Beer, a close military aide of Ben-Gurion's, who was caught delivering confidential documents to the Soviet embassy.

Beer, whose true identity was never established, died in prison. The case was significant, for it showed the extreme difficulties that Israeli intelligence encountered in the days of mass immigration, when a man like Beer, who presented himself as a Jewish student from Vienna and claimed to have extensive military experience, could quickly gain a high army rank and the general confidence and friendship of the prime minister.

It was Harel's major success when he proved that the real Israel Beer had died in Vienna many years before, and the man whom he had exposed was a Soviet spy.

Harel's biggest triumph was his personal supervision of the operation to capture the chief Nazi war criminal Adolf Eichmannn in Argentina. Harel resolved that "if Eichmannn were alive, come hell or high water, he'd be caught." He was disappointed, however, when he found Eichmannn to be a scared little official with a slavelike mentality.