Robert Frederick Cohen was born on May 14, 1916 in Vancouver, British Columbia, the son of Moise Jacques Cohen, an electrical engineer, and his wife Hattie Alberta née Mackay, a school teacher. He was named Robert after his maternal great uncle Robert Wood, and Frederick after Frederick Alexander Christy, the second husband of his maternal grandmother. He had an older brother, John, who was born in 1913. Moise changed the family surname to Christy by deed poll on August 31, 1918. On November 4, Moise was accidentally electrocuted at work. Hattie died after goitre surgery in 1926. Christy and his brother were then cared for by Robert Wood, their grandmother Alberta Mackay, and their great aunt Maud Mackay.