Reuben Zaslani (1909–1959; later changed his surname to Shiloah) was born in Jerusalem and spoke Arabic. In 1949, then Prime Minister and Defense Minister David Ben-Gurion appointed him the first head of Mossad, a post he held until 1952. (Some sources say he set up Mossad in 1951; perhaps the agency was not called Mossad initially). He then took up a senior post at Israel’s Embassy in Washington and became a political adviser to the Foreign Minister.
He was involved, since his youth, in covert Yishuv affairs and was close to its leaders. He was confidant of David Ben-Gurion and Moshe Sharet, particularly in political matters.
Rashid Khalidi writes (The Iron Cage: The Story of the Palestinian Struggle for Statehood, p. 75):
Perhaps the most eminent of the four, Reuven Zaslani, eventually became the founder of Israel's external espionage agency, the Mossad. Zaslani later changed his name to Shiloach, and the Middle East Center at Tel Aviv University (now the Moshe Dayan Center) was named for him for a time. The two names that this center has borne illustrate the intimate (and thoroughly unselfconscious) relationship within Israel institutions between academic study of the region on the one hand, and both intelligence work and warfare directed against the Arabs on the other
See this Wikipedia (English) article
See this Wikipedia (Czech) article (English translation)
See this Wikipedia (Hebrew) article (English translation)
See this Wikipedia (Polish) article (English translation)