Here is a brief bit of information Parker. Dates don't seem to make sense.
Source is the American Civil War Database.

His CSR files should allow you to fill in the rest.

George Martin

O S. Parker

Residence was not listed;
Enlisted on 4/6/1865 at Bowling Green, KY as a Private.

On 12/3/1864 he mustered into "B" Co. KY 17th Cavalry USA
He was Mustered Out on 9/20/1865 at Louisville, KY