According to Social Security records, Gerald Hamilton was born in New York on January 1, 1928 and was the son of Marie Grinnan. His father was most likely Tyler Garner, who his mother married a month after his birth. His father, Tyler, died in May, 1930 in Manhattan at age 20. Gerald's social security records indicate that in the 1950s he used the name Jerry Garner. However, his social security death record lists his father as Aubrey Hamilton. Aubrey Hamilton is also listed as Marie's spouse on her social security records, so, it is likely that Mr. Hamilton was his step-father.
Gerald's grandfather on his mother's side (his mother's father), Milo Grinnan, was born into slavery in Richmond, Virginia in 1853. He died in 1918.
Sources: U.S. Census Records, U.S. Social Security records, NY City marriage records, NYC death records, U.S. Freedmen's Bank Records, National Archives.