Benjamin Garner Sr. was in the 7th Texas Cavalry. Family legend says he lost a leg in the war. He died before 1868.
His wife had "run off" before he died, so Benjamin Jr. was left an orphan. He was taken in (or was he bought?) by another family who mistreated him and used him as a servant. He grew up very resentful.
Ben jr's age, place (Cooke or Grayson county vicinity probably) and circumstance makes him a prime candidate for being an auction child.