Be·gin (bā'gĭn) Russian-born Israeli politician. He led (1943-1948) Irgun, the Zionist underground movement in Palestine. After the establishment of Israel, Begin became a political leader known for his hard-line views on the Arabs, but as prime minister (1977-1983) he strove to resolve the Arab-Israel conflict. He shared the 1978 Nobel Peace Prize with Anwar el-Sadat of Egypt.