Blake wrote:
Henry Halleck
Henry W. Halleck was a military scholar who did much to create and promote the quasi-Napoleonic war-fighting doctrine that dominated the officer corps on both sides of the Civil War. He also did much to promote an ethos of military professionalism. Despite his academic and professional achievements, however, Halleck was an unimaginative, overly cautious tactician, whose views on the nature of warfare lagged behind the realities of modern combat fought on massive scales. As general-in-chief of the Union armies, he defined his role too narrowly, functioning as an administrator rather than a genuine military leader. Too often, he impeded rather than aided the field commanders (including Grant) who reported to him. Although he proved to be an able administrator, logistician, and liaison between civilian and military leaders, Halleck was personally arrogant, defensive, aloof, uninspiring, and unsupportive. Nevertheless, after (at his urging) Grant was appointed general-in-chief of the Union armies, Halleck invented the role of chief of staff, singlehandedly creating the modern concept of the staff officer and thereby profoundly influencing the ways America would fight future wars, especially in the twentieth and twenty-first centuries.
HISTORIANS RATING: TWO STARS
Okay. Two stars. I am indifferent towards Halleck. In my mind he is just an inept general who got lucky enough to be Grant's senior and steal his credit early in the war. His later accomplishments as a chief of staff save his reputation.
I think your historian is giving Halleck a lot of undue credit there.
Credit for the creation of "the modern concept of staff officer" must surely go to Prussia very early in the 19th century in response to their massive loss to Napoleon at Jena (although Prussia had staff officers for over a century before that). Particular credit for that creation should go to Scharnhorst and his compatriot Gneisenau [interestingly, both had WWII battleships named after them].
As for "Halleck invented the role of chief of staff": that's complete rubbish. Gneisenau was appointed as Blucher's Chief of Staff in 1815 and that was very much in the modern concept of staff officers that he and Scharnhorst had invented and developed after Jena.