gillon was born in jerusalem. his mother, saada gillon (née frumkin), was born in palestine. her ancestors had come to palestine from the russian empire in the 19th century. gillon's maternal great grandfather was israel dov frumkin, a pioneer of hebrew journalism in palestine who had moved to palestine from russia in 1859. his maternal grandfather, gad frumkin, was one of the first trained attorneys in palestine, who was the only jewish judge on the supreme court of palestine during the british mandate era and was also a member of the hebrew university of jerusalem's board of governors from the 1930s until his death. his maternal grandmother, chana frumkin, was the daughter of aharon eisenberg, a pioneer of the first aliyah who was one of the founders of rehovot, and was the president of b'nai b'rith in jerusalem. his mother served as deputy attorney general. his father, colin gillon, was born colin gluckman to a jewish family in johannesburg, south africa, and immigrated to palestine in 1937. gillon's paternal grandmother, katie gluckman, was a prominent activist in the zionist movement in south africa. colin served as state attorney, and hebraized his name from gluckman to gillon at prime minister david ben-gurion's insistence.