Now that's a sneaky answer, Roger, 'cause all military folk are civilians at some point in their life. Assuming that this person is tied to Lincoln in some respect, was he military or civilian at the time of their interaction?
'both civilian and military' ... so maybe involved with War Dept or Indian administration ? (and a Mark Twain impersonator)
... on the other hand could be nothing whatsoever to do with my above post ... Henry Sands Brooks (supplier of uniforms as well as gentlemens attire) and wife Lavinia?
Kudos, Michael! Indeed the lady is Mary Harlan Lincoln. But the man is not Larkin Mead. Mead, the designer of the Lincoln Tomb, is the man who created the two sculpted portraits. So who is the man in the initially posted image?