Forster was born Robert Wallace Forster, Jr. in Rochester, New York to Grace Dorothy (née Montanarella) and Robert Wallace Foster, Sr., who worked as an elephant trainer for the Ringling Bros. and Barnum & Bailey Circus and later as an executive for a baking supply company. The two divorced in 1949. As a tribute to his father, Forster was allowed to hang one of his father's Barnum & Bailey Circus posters in the office of his character "Max Cherry" in the Quentin Tarantino film Jackie Brown.
Forster recorded a public service announcement for Deejay Ra's 'Hip-Hop Literacy' campaign, encouraging reading of books by Elmore Leonard (he starred in the movie adaption of Leonard's book Rum Punch, Jackie Brown). Mr. Forster is also a motivational speaker.