Family
- father Robert Wallace Foster: Formerly worked as an elephant trainer with Ringling Bros.; later began working as an executive for a baking supply company; divorced from Forster's mother c. 1949
- mother Grace Dorothy Foster: Divorced from Forster's father c. 1949; committed suicide in 1966
- son Robert Foster: Born in 1965; mother identified only as Marlene
- daughter Elizabeth Foster: Born in 1967; mother, June Provenzano
- daughter Kate Forster: Born in 1969; mother, June Provenzano; played father's niece in "Hollywood Harry" (1985)
- daughter Maeghen Foster: Born in 1972; mother, June Provenzano
Companions
- Dani Janssen: widow of David Janssen; dating
- Marlene: mother of Forster's son Robert; Forster told the New York Times in 1972 that he was not married to the mother of his son
