Grandpa Sawyer is the grandfather of Drayton, Chop Top, Nubbins, and Leatherface. He is extremely old and frail, but the family still thinks he is the best killer of them all. He at first appears to be a corpse and has the inability to talk. He, like the others, was fired from his job at the slaughter house when they started using the airguns.
Despite his extreme age and fraility the family hold him in great regard and want him to have the "honor" of killing their victim, putting her through an agonizing torture regime in which the stronger family members held her over a sink whilst Grandpa was given a small hammer which he continually dropped: eventually Drayton decided to help Grandpa out and hit the victim with the hammer, however before he could finish the job their base was raided by the vengeful brother of one of their former victims, who attacked them with a chainsaw.
Grandpa tried to defend Leatherface during the over-the-top battle that occured but his fraility and age showed as he took extreme effort to throw the hammer - even then only succeeding in bouncing it off Leatherface's head instead (much to Leatherface's displeasure).
It is unknown what happened to Grandpa but he very likely died in the explosion caused when Drayton released a grenade in vengeance for quite literally having his rear cut by a chainsaw.