While reviewing the digital image of a record from the Ancestry.com collection, "Georgia, Property Tax Digests, 1793-1893," I found this phrase several times on the page: "Do agt for" followed by a person name.
I'm not even sure that I'm transcribing it right, so I'm including a picture which shows 2 occurrences.
I suspect there may be an abbreviation involved. I suspect that understanding this entry may give a hint to the relationship between the names involved.
According to Ancestry.com, these records represent the "tax digest books for 135 Georgia counties from 1793 - 1893." For those with Ancestry.com access, you can see the entire page here