Tunnell grew up in the Garrett Hill neighborhood of Radnor Township, approximately eight miles northwest of Philadelphia. His parents were divorced when Tunnell was young, and he and three siblings were raised by his mother, Catherine, who worked as a housekeeper in the homes of wealthy families in the Philadelphia Main Line area. His sister, Vivian, recalled Garrett Hill as a multi-ethnic neighborhood where "everybody mingled", and her brother "learned from his environment – be yourself, but adapt to others who might be different in the group."