Robertson was born in Scarborough, Ontario. He is the youngest of five children, with two sisters, Lynn and Bonnie, and two brothers, Bill and Doug; He claims to have been named on a bet. His mother, Wilma, was a secretary for Imperial Oil, and his father, Earl, worked both as a shipping foreman for Honeywell, and as an egg grader. He believes that his conception was an "accident" because he is several years younger than his siblings, who were all born about one year apart. He credits this situation with allowing him to have the experience of being both in a big family, and an only child—once his siblings moved out of their home.