A book came out a year or so ago on the subject. Which I might have read if not for a long argument with the author suggested dubious conclusions about Lincoln, in 1861, being ready to indiscriminately bomb civilians.
Adjutant General of the Army. Though he was briefly Secretary of War during Andrew Johnson's administration. He was also Winfield Scott's last chief of staff (1853-1861).
His predecessor as Adjutant General? Samuel Cooper, who took the same role with the Confederate Army, and seems to have been deliberately sidelined by Jeff Davis for most of the war.
A dual biography of Thomas and Cooper might be worthwhile. They were only six years apart in age. Cooper was born in Virginia; Thomas was born in Delaware. Both were West Pointers, but neither did very well - Thomas in the middle of his class and Cooper near the bottom.
The parallel careers of Union Gen. George Sears Greene (May 6, 1801 – January 28, 1899)
and Confederate Col. Isaac Williams Smith (1826-1897) would make for a good read, both were engineers, both served in the war, on opposite sides, and both were railroad engineers, both designed advanced drinking water systems and civic utilities systems that are still in use today.
Smith is the lesser known of the two, here is a short biography of Col. Smith
Actually Michael Eggleston wrote President Lincoln's Recruiter: General Lorenzo Thomas and the United States Colored Troops in the Civil War which was published by McFarland in 2013
Actually Michael Eggleston wrote President Lincoln's Recruiter: General Lorenzo Thomas and the United States Colored Troops in the Civil War which was published by McFarland in 2013