You didn't include any dates, or approximate dates, in your query, they are important.But, because of unusual middle name I went looking.
Combined info from TX Dth Idx Online, and SSDI:
Rubin Isham Fitzgerald, b 11 Feb 1909; d 16 Mar 1982 Hopkins Co, TX; last residence Sulpher Springs, Hopkins Co, TX; SS card issued in TX.
Rubin Isham Fitzgerald, Jr, b 10 Nov 1939; d 1 Sep 1996 Dallas Co, TX; last residence Lancaster, Dallas Co, TX; SS card issued in TX.
With date and location of death of Rubin, Sr, you can obtain a copy of his death certificate, which should show the names and birth locations of his parents.Once you have the name of his father, you can check the 1910 census when Rubin,Sr. would be a youngster in his father's home.Plus, the 1920 census, too.You will pick up more family info, and other children in the household, also.